As mentioned in the CS18AI Manual on Section 4 the microphone and line inputs when connected to a RM Series mixer are as follows:
Mic/Line input 1/TB is assigned as the source for the StudioLive RM mixer Talkback. It will also be available as the network source for Input 31 of the RM mixer.
Mic/Line input 2 is unassigned by default but will be available as the network source for Input 32 of the StudioLive RM.
Line inputs 3 and 4 are assigned as the stereo Digital Return input of the RM mixer.
In order to control the level of those inputs, the control is done from the Talkback Edit page (see section 5.5) and level controls are on the input control page.