Construction advice..weight issues

Thanks for the wonderful site, I have learned a lot of information from all of the posts. This is my 1st post so please forgive me if I make a mistake or give too much/ little information, but I am at a bit of a loss as to how to proceed soundproofing my room. I am trying to soundproof a room in a "pre-war" apartment building in New York City. I plan on using the room mainly as a home studio (film and TV music) as well as a practice room (woodwinds, guitar, etc...). The room is going to be 12.8'X10.9' with aprox. 9' ceilings. The floors of the apartment building are apparently 6'' concrete slabs that only permit 40 lbs per square foot. I am not going to be rehearsing loud rock bands in this room (saxophone will probably be the loudest instrument played) and I don't generally mix at loud levels (I also only use near-field monitors). The only "walls" that I share with neighbors are the floor and ceiling as all the other walls are either interior, lead to the adjacent building, or face a common courtyard. I have hired a very experienced and reputable soundproofing contactor who submitted a very thorough plan: Floor: Construct floating floor consiting of 2 layers 5/8'' gypsum board and 2 layers plywood on kinetics isolation pads. Walls & Celings: Construct new walls and celings consiting of 3 layers 5/8'' gypsum board on metal framing with mineral wool insulation batts between framing. Doors: Install 2 metal wrapped gypsum core doors Windows: Install new inner wall 1/2'' laminated glass windows and box out and duct A/C unit. Unfortunately the weight of the materials in this plan exceed the 40lb per sq. ft that is permitted. Even when we reduce the materials to two layers gypsum board and plywood on the walls and ceilings and 1 layer on the floor we are very close to exceeding the weight limit. I'm concerned that if we reduce the amount of materials even more that the room won't be adequately soundproofed, thouigh perhaps for my needs, it will. Or perhaps there is a different approach altogether? Any advice would be greatly appreciated. Thank you