As I understand it, TC Helicon harmonizers can auto adjust harmonies for MIDI. I use a keyboard workstation for my backing music with the drums and bass programmed in.
If I connect the keyboard to the harmonizer, will the harmonizer then pick up the backing files and auto adjust the harmonies or does it only work with MIDI?
Let's put it this way: MIDI is a standard, but each keyboard or sequencer may have it's own setup; generally speaking, the harmonizer will be responding to whatever MIDI the keyboard (or sequencer) is transmitting, so the first thing to check is what's being sent through the MIDI OUT, and whether it's just the chords you're playing or any data related to the backing tracks as well.
If the keyboard is only transmitting the chords you're playing (or chords from a pre-recorded track), you're all set.
If the keyboard is transmitting more than that, you should check into whether it's possible to disable some of the other data, so you're just passing relevant MIDI Note On/Off to the harmonizer.