Not a SL 16.4.2 or SL 1642 AI, but a SL 16 or SL 32SC... Two mixers do not necessarily expand the number of input channels. Most of the Series III consoles are 32 channel mixers, only the SL 64S has 64 channels and 32 flex mixes. You can only add 8 more physical input channels to your SL 24.