I attemoted to substitute a real track with a midi synth patch. I tried both the piano and guitar tracks. It would not work. I just picked a style so I could here the patch . Can you only sub midi for midi?
Yes... if you want to hear a midi synth patch, it's necessary to have midi data on the track. Since Realtracks are audio, they are not capable of sending any midi information to drive a synth.
The exception would be in Realband where it's possible to load a RT's notation onto a separate track (if the RT has notation associated with it). Since this notation is midi-based, it could be used to control a midi synth on this track that contains notation.