Best thing is to send all the things you want to loop to the same bus, no extra hands or feet needed!
Here is my setup:
Audio 1 in (guitar) to Bus 1
Audio 2 in (vox) to Bus 1
SL sidechained with Bus 1 (input audio set to --infinity db)
Bus 1 output to Main Out
SL to Bus 2
Bus 2 to Audio track 3 (so can record mix)
Audio track 3 output to Main Out
I use SL / Logic as a writing tool where I set the song recording 3 audio tracks so I have unlooped tracks for later editing.
Great program this btw!