Huh. First forum I've seen that makes you go back to the index page to log in.

Anyway, I'm not sure how Aria uses that, but it's probably not through those GM sounds. Good sample libraries like Aria have this kind of expression available. I haven't messed with it, but I think that you use them by playing special MIDI notes. This again is something that you need a more powerful sequencer for. Possibly, if you were able to sequence a melody that uses such expression, you could then save that melody as a MIDI file, and import it into a BIAB song. I don't see any reason why this wouldn't work, but then, a lot of things don't work the way I'd expect.