just one quick confirmation,
are you aware that the setting is twofold? the preenfm is 4 part multitimbral, so you set midich1 to a channel and midich2 to a channel (via the rightmost encoder).
the notes sent on channel 1 should still sound when midich2:2 is enabled, but they should only go to channel:1.
so to summarize you can set the preenfm2 to for example:
midich1:1
midich2:2
midich3:10
midich4:6
this would play your synth 1 on preenfmchannel1, synth 2 on preenfmchannel2 and drums 1 to 4 on preenfmchannel3 (which does not make much sense)
i hope this helps!
if you see the 2 flashing on the preenfm2 that means that channel two eceived a note and it indeed has to be either no preset loaded or voice number set to zero. try loading a (different) preset in voice 2 or adjust voice number