No mixing is done in Capture directly. Instead, the individual outputs of each audio track in Capture are hardwired to the FireWire returns for each corresponding input channel on the StudioLive mixer.
Thus, with the FireWire returns engaged for each input channel on your StudioLive mixer, the output of your multitrack Session is routed to the StudioLive mixer, where it can be mixed just like any other audio inputs.
For information on doing a mixdown using Capture though, see sections 2.5 FireWire Sends and Returns and section 3.7 VSL: Setup Tab for the section about the Auxilliary inputs router (or the Flexible Inputs Router on the 16.0.2) in the StudioLive Software manual:
See also the section 6.6 Mixing Your Session in the same manual.
The process works as follows:
1. 24.4.2 owners: In VSL, select “Main L/R” for Auxiliary Inputs 25 and 26.
16.4.2 owners: In VSL, select “Main L/R” for Auxiliary Input 17 and 18.
16.0.2 owners: In VSL, patch “Main L/R” to Flexible Inputs 15 and 16. Please Note: if you wish to create a mix using Capture, you will not be able to record using analog inputs 15 and 16.
2. Be sure that Record Arm is disabled for all audio-input tracks in Capture and that the FireWire returns for all input channels on the StudioLive mixer are engaged.
3. In Capture, select the Auxiliary Stereo Track (StudioLive 16.4.2 and 24.4.2) or Track 15/16 (StudioLive 16.0.2) and enable Record Arm.
4. Bring the playback-cursor position to the beginning of the Session by clicking the Return to Zero button in the Transport.
5. Activate recording by clicking on the Record button in the Transport; the playback cursor should begin to move from left to right, and audio should be playing through each input on the StudioLive mixer. The Auxiliary Stereo Track in Capture should be recording a new audio event, which is the post fader main mix from the StudioLive mixer.
The new audio event that has been recorded from the StudioLive mixer will be stored as a stereo WAV file at the sample rate to which the StudioLive mixer is set. It is possible to export this file, and any other audio files from Capture, to another storage location (such as a backup hard drive), as discussed in section 6.8 Export Audio Files in the StudioLive Software Library Manual.