STEP 1: Insert a multichannel virtual instrument plug-in on a MIDI track.
STEP 2: Create a group of MIDI tracks for the sub-instruments (channels) you want to freeze.
STEP 3: Insert an External Instrument on each sub-instrument track and route it to the virtual instrument plug-in.
STEP 4: Create scenes or an arrangement
STEP 5: Freeze the MIDI sub-instrument tracks to reduce CPU load or preserve random elements.
STEP 6: Consolidate audio freeze files in Arrangement view to convert the bit-depth to the setting in Live's preferences.