This sounds like something my Dad wants to do with HIS PTPA setup- would latency problems arise if:

You play a MIDI file thru an external TC box, and send the audio back into PTPA to record it? In other words, sing and record harmony to a pre-recorded MIDI file.

BTW, do NOT base your thoughts about TC Helicon's stand alone harmony boxes, on the one in BIAB and PTPA. The stand-alone boxes sound like VOICES, not like a robot being cut up by a bandsaw! I plan to get one of the new Harmony-G XT boxes. Jeff Law at Sweetwater sells them for $219. (The G is for guitar players. The M is for keyboard players, and that one costs $299.)

Another "wish"- being able to record a MIDI track AND and audio track, at the same time!

Rusty