TM,
i doubt you want to go this route.
the first thing is, it is going to be extremely heavy. are you planning to support the inner walls and ceiling on this floating floor? have you calculated what this structure plus all your equipment/furniture is going to weigh? can your house's floor support this?
not without major upgrading of structure, is my guess. maybe steel beams. maybe not. but serious upgrading. would you put a 500 gallon hot tub on the second floor without reinforcement, i don't think so.

this is a question for an engineer.
but if you do get an enginner and decide to do it safely, make sure that you make the inner and outer leaves of your floor very thick, at least 3 or 4 sheets of 3/4 inch plywood each. if you do this and have a large (say 8 inch) airspace you MAY get the cavity resonance down to a reasonable level. you can calculate this based on the actual materials and airspace you are using.
see this link for a good calculator
http://forum.studiotips.com/viewtopic.php?t=1522
if you create a cavity with too high a resonance, it makes the floor LESS soundproof at that frequency and the surrounding frequencies, and can mean that you wasted your time, money and headroom. below resonance frequency, the floating has no effect. so you must keep the resonance frequency low by making the leaves heavy and the airspace big.
dan
