as for your first paragraph: Actually, that's exactly what I do. When I want to only hear ONE track (whether it be audio, midi, effect, group, etc.) I solo it in the main composition window.

and your second paragraph: GYEH?!
Let me see if I have your process correct.
- open new midi track and assign a synth(1) to that track on channel 1
- open another midi track and assign a DIFFERENT synth(2) to channel 2
- when your sequence is playing it's playing synth(2) with the input from channel 1?

for argument's sake lets say synth 1 is NI Massive
and synth 2 is FM7

If this is the case make sure that when you setup your midi track for FM7, to select the "midi out" for that synth and not for Massive.

Hope this helps