Could you have the drums come out of the 3 and 4 outputs (I can't remember what they call these on Yamahas) - that is, have the drums come out of the extra set of output jacks, then have a little mixer - and you can make the drums any volume - and leave 'em that way ... for your show?

This is something I did with my Technics KN-7000: I had drums and bass come out of outs 3 and 4, and the rest of the keyboard out of 1 and 2. Then I could turn up (or down) my "rhythm section" (drums + bass) very easily if I sensed they needed a tweak in a given hall, with the band crankin', etc.

I think you can do this on Tyros as well ... it does however require a couple of extra cables plus a small mixer ... but give some nice real-time, live flexibility