Thanks for the feedback (and for the chart)! As far as I can tell from talking with the Owens Corning manager, the R19/RC/drywall is their standard basement system ceiling. (HVAC ducts, pipes, and beams below the joists are boxed out with pine--and yes, the space between the bottom of the joists and the bottom of the floor above is large, about 25 cm.)
The Owens Corning manager suggested the Homasote/no RC option, because we expressed concern that the "standard" ceiling would not dampen the sound enough. (The OC salesman had told us that we would need "extra sound deadening" for the ceiling on account of the drum kit.) The OC manager (different guy, of course) doesn't know any more about acoustics than I do--he said this option was suggested by his "technical experts," which could just mean a half-hour surfing the web.
What would you do in our place?
