Hi Richard,
you can do both.
Record the individual channels via the Ip Direct Outputs or tielines.
Via tielines:
Go to the I/O screen->Tielines->Local (or SLink if you have a stagebox connected). In the top row go USB and patch all the channels you want to record
Via Direct Outputs
Go to the I/O screen->Outputs->IP Direct Outputs. In the top row go USB and patch all the channels you want to record
For you MainLR outs:
Go to the I/O screen->Outputs->MixOut. Here you´ll find all Mixes (Groups, Auxes), Matrices and your MainLR. In the top row go USB and patch your MainLR to two USB outputs, you haven´t used up.
Remember: 32 is the limit for USB recording. If you want to record your MainLR, you can “only” record 30 individual channels.
Hope that helps.
Cheers,
André