partial subfloor mass - waste?

So as I get closer to breaking ground.. I've realized something. While my joists can handle the additional weight, I realized that I will not be able to add mass to the subfloor over the entire room, but the area where I cannot add it will be over the largest air mass. Detailed explanation and diagram: The room will be approximately 10', with the front of the room sloping down to approximately 7' (see diagram) both for acoustical purposes as well as to avoid existing ductwork, pipes, etc. I realized that I would have to completely remove all the aforementioned ductwork, pipes, etc to get up between the joists to add mass to the subfloor above them - which may be more trouble than it's worth. The area in the diagram that is RED is the area that would be very difficult to get to. So - if I can't add mass to the subfloor all the way to the vertical wall, is it a waste? Or should I add it where I can?

You haven't build your innerroom yet, did you? So the only thing that's in the way is ductwork. Hmm, you might wanna box it in, tho it will create a 3th leaf effect, it seems one of those "you've gotta work with what ya got" situations. Could you post some photos of the area to give us a better view on this situation?

There's a picture if you scroll down a bit in this thread viewtopic.php?f=1&t=11551 There's a bunch of ductwork, a natural gas pipe - but also a lot of wiring passing up through the subfloor above where the ducts are (I'll try to get a picture of it) that would be hard (if not impossible) to seal up.

Anybody? Here's a photo of the area in question..

I reckon Brien has the right idea: If you cannot get access, then just box it in with plenty of drywall, even though you'll have three leaves there. Make up for the reduced isolation with more mass on the two leaves that you can get to. - Stuart -

Well - I'm not sure I can box this all in for a few reasons.. the big one is - these are the main HVAC trunks for my house - which I need to run ducts from (one exists already) into the two rooms I'm building.. so I'd be boxing them in, then punching two holes immediately. Another issue (less of one, though) - I'll be running the ceiling joists under this ductwork.. and boxing it in will eat up a few more inches of ceiling height.. minimal, but still..