that's all great absorption material, and adding mass is always good, but in order for those materials to do their job you need an airspace between the rooms, and between the rooms and the exterior structure. in plain english this means double walls with an airspace between them. and for serious isolation you need to isolate the floor as well, and then construct the walls on that isolated surface. this is where the term "floating" rooms comes from--they don't have any contact (or at least very little) with the building's actual structure, or each other! ie: they float...
how much isolation are you aiming at, and what has your engineer promised you in terms of decibel reduction with your current design? worth investigating--my hunch (based on the pics and sketchup files) is that you're not going to get anywhere near what you'll need if you're planning to track acoustic drums and big amplifiers etc...
again, not trying to rain on your parade! but it would be a shame to invest alot of money without getting the results you need... please discuss this with the engineer before you get any further into your construction!!
fingers crossed for you bro...
ps - amazing pic of Gisele Bundchen !