If you connect your console to your laptop/PC/Mac via the USB port and adjust your computer's settings to see the DN32-LIVE as a sound card, it will only pass two channels of audio (effectively your stereo Left & Right outputs from the console)

If you wish to access all 32 channels of audio, this can only be done via the set-up of your chosen DAW (Digital Audio Workstation) on your computer such as Cubase, Protools, Reaper etc.

Recording via USB is an additional means of recording and has no impact on the ability to record to the on-board SD cards.