How was the experience of;

A) Playing along with the SMF with some Instr. muted?
Any tips?

The idea is to play on top of the SMF so we can use the horn and some of the other tracks

As for all this other stuff... WHATEVA gets the job done! Except if you are talking about someone PRETENDING to play... that's just BS imho. But I and my audiences have no problem if I play on top of the MIDI file... just like they don't care if I use a Harmonizer... whatever sounds good and gets 'em dancin!