Need soundproofing advice for unusual room

I hope some of you knowledgeable folks here can give me advice. I'm in the middle of having an addition built (basement, media room on main floor, bedroom w/bath on 2nd floor). I need to soundproof the media room so noise doesn't travel upstairs to the bedroom, am not so concerned about sound to the rest of the floor the media room is on. The framing is already done and I realize now, after a lot of reading on this forum, there are things I should have done before now, that would have helped more with noise control.

There is a 22' common wall between the addition and existing house, plus a common 4' section of an adjoining 18' wall, the remainder of which is exterior. The common wall is double framed, but unfortunately was built with no air space between the frames. The furnace is in the basement below. There are 3 supply ducts for the bedroom/bath that run up through the common wall and across the media room ceiling in joist cavities, and a return duct for the bedroom that runs straight up the common wall. All the media room supplies are in the floor, and there's one return at baseboard level and one at crown molding level (on common wall).

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