As a bit of follow-up, I did a few experiments to make sense of the reason that no ReWire outputs are available when NOTION 4 is running as a ReWire 2 slave in a ReWire 2 session, which for reference initially appeared to be a bit strange . . .
NOTION 4 Running as ReWire 2 Slave to Logic Pro X ~ No ReWire Outputs AvailableBACKGROUNDAs a general rule, when apparently strange things begin happening after trying to discover how a new application does ReWire 2, it is a good idea to do a warm boot or perhaps a cold boot, and this certainly applies when one is doing digital music production on the Mac, but I also think it applies in the Windows universe, although I have no way at present to confirm this . . .
The reason for doing a warm or perhaps cold boot is that a lot of stuff happens behind the scenes and some of it involves working with aspects of the operating system with what one might characterize as "elevated" privileges, which is not a problem so long as everything is designed and coded correctly, including error handlers, but this is not always the case, and when something is done that in one way or another makes no sense to the gnomes who are responsible for designing and coding error handlers, then some patently strange things can and usually do occur, and the only way to return the operating system and ReWire 2 specific infrastructure back to pristine condition is to reboot the computer, because one of the things that happens involves what colloquially are called "ghost processes" . . .
Observing that I focused on application development in the Windows universe beginning in January 1987 with the first version of Windows and continuing until December 2001 when I started the switch to the Apple universe--hence I tend to use colloquial terminology from the Windows universe when discussing deep operating system internals--what happens in the Windows universe is that when a Dynamic Link Library (DLL) has a particularly gnarly bug that when activated causes the application which "owns" the DLL to crash, the application never has the opportunity to unload the DLL that it "owns", and the operating system also in this scenario does not have the opportunity, hence there is a DLL that for all practical purposes thinks and behaves as if it continues to be "owned" by an application, which is a problem because (a) its "owner" application is gone and (b) the unique identifier of the "owner" cannot be replaced by a new identifier when a new instance of the "owner" application is started, hence the "ghost process" is orphaned and cannot be adopted, which is another way to explain what happens, and the only solution is reboot the computer . . .
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NOTE: In Mac OS X, a Dynamic Link Library (DLL) is called a "Shared Library", but the concepts are the same, although Mac OS X is built on top of UNIX, which makes it a bit different in some respects, except that Windows is built on top of MS-DOS or whatever, which basically is not do dissimilar from UNIX, but so what. Mac OS X and Windows are like Coca-Cola and Pepsi, and as such for all practical purposes they are peas in the same pod . . . ]
Most of the time, this does
not happen in the Apple universe, in part because Mac OS X applications run in a type of protected space called a "sandbox", where the "sandbox" is a strategy used by the operating system to protect itself from badly behaved applications, which is excellent except in certain conditions where an application can engage in bad behaviors outside of its "sandbox", which is one of the things (a) that can and does happen in a ReWire 2 session and (b) that in some respects is a natural consequence of the "elevated privileges" required by the ReWire 2 infrastructure or whatever . . .
Rather than do a cold boot, I did a warm boot, but the computer would
not do a warm boot, because Logic Pro X was reporting that there was a ReWire 2 slave application running, except that doing a Force Quit to see which application was the culprit showed that there were no other ReWire 2 applications known to the operating system and that Logic Pro X was the only application running that used ReWire 2, which was an excellent clue and verified the vast wisdom of recognizing that the computer needed to be rebooted to clear a "ghost process", hence I zapped Logic Pro X via Force Quit and then did the warm boot . . .
After the warm boot completed, I started NOTION 4; created a new project with one VSTi virtual instrument staff; and then switched to the NOTION 4 Mixer, where I tried to create a ReWire output channel, which worked as expected, as shown in the following screen capture . . .
NOTION 4 Running Standalone ~ ReWire Outputs Are AvailableFor reference, before the reboot when NOTION 4 was running standalone, it behaved the same as it did when it was running as the ReWire 2 slave to Logic Pro X, which was the unusual behavior, since there are three scenarios where NOTION 4 can create ReWire outputs, but none of them were working prior to the reboot:
(1) NOTION 4 is running by itself with no other ReWire 2 applications running . . .
(2) NOTION 4 is running as the ReWire 2 host controller for a ReWire 2 session . . .
(3) NOTION 4 is running by itself but another application that only can function as a ReWire 2 host controller is started after NOTION 4 starts and NOTION 4 has become the defacto ReWire 2 host controller, which is the scenario when NOTION 4 is started first and a DAW application like Digital Performer 8 or Logic Pro 9/X is started, where Digital Performer 8 and Logic Pro 9/X only act as ReWire 2 host controllers, hence in this third scenario simply do
not participate in the offered ReWire 2 session. For reference, this is not what happens when Live 9 (Ableton) is started, since it can participate in a ReWire 2 session as a ReWire 2 slave, although with limited functionality, and is the reason you see "Ableton Live" in the list of ReWire output candidates, but you do not see Digital Performer or Logic Pro 9/X in the list of ReWire output candidates . . .
As noted, after the reboot, all three of the aforementioned scenarios worked as expected, and the create ReWire outputs option was available in NOTION 4 . . .
Additionally, I verified the "No ReWIre outputs available" behavior when Digital Performer 8 was the ReWire 2 host controller and NOTION 4 was the ReWIre 2 slave, hence the "No ReWire outputs available" is the expected behavior when NOTION 4 is running as ReWire 2 slave . . .
THOUGHTSThis was a FUN set of experiments, and in retrospect I though it was strange because it was
not something I would do, but it also was strange due to the particular sequence of events I tried while attempting to discover how Logic Pro X does ReWire 2 being similar to the set of things you tried, since we encountered what I think is the same set of strange behaviors . . .
ReWire 2 is an excellent technology that makes some simply amazing interactions among digital music production applications possible, but it is very persnickety with respect to all the options, parameters, actions, and so forth being done correctly, and the fact of the matter is that due to its vast power which comes in part from having and needing certain "elevated privileges", even an apparently tiny and insignificant mistake can cause big problems . . .
IMPORTANT: The key to working successfully with ReWire 2 is to follow all the rules precisely, and when this is done on the Mac, ReWire 2 is rock solid, for sure . . .For sure! I am planning to provide some screen captures and to do a YouTube video to show you exactly how to do what you want to do, which will take a while, but probably not too long, and it is easier than it was with Logic Pro 9, although a few things are different . . .
Lots of FUN! 
P. S. None of what I explained about ReWire 2 includes any proprietary information, which should be obvious to those folks who have done low-level C/C++ software engineering for applications in a transaction based (a.k.a., "event driven") operating system like Mac OS X and Windows . . .
These are links to the public information regarding ReWire 2 at the Propellerhead Software website, and if you know a bit about operating system internals, then it is not so difficult to connect the dots . . .
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NOTE: There are two excellent diagrams at this link . . . ]
ReWire Technical Information for Developers (Propellerhead Software)What is ReWIre? (Propellerhead Software)In this respect, by design I was a bit "fuzzy" in the way I explained everything, since as a registered ReWIre Developer I have access to all the internal details under NDA, although the way I explained everything is close enough and probably is vastly more information that most digital music production composers want to know, anyway, but so what . . .
So what!
The important things are (a) that NOTION 4 and Logic Pro X are following the rules for ReWire 2; (b) that you can do what you need to do; but (c) that you need to do it in a particular way, which is excellent, for sure . . .
For sure! 