It's easier to devise a game plan before the ninth inning!
Sound-dampening drywall such as QuietRock and the do-it-yourself version, Green Glue, are just two ways of achieving the same goal. Resilient channels depend on getting every detail right; one or two screws too deep and the whole thing is short-circuited.
Extra insulation in the walls and between floors, including mineral wool (Roxul) has a negligible effect on air-borne sound. Indeed, a National Research Council of Canada study notes that "Using sound-absorbing materials in a rigidly connected assembly is a waste of money." But it's easy and some builders love to upcharge big for it. Gypsum floor underlayments work well, but you may be too late for that. Ditto internally dampened QuietWood floor panels.
Save the money on cast iron drains; instead, frame around and use lots of insulation. (There's a good thread here somewhere on various methods.) For supply pipes, add the slip-on foam to all the runs; this also moderates the annoying seconds of ice water you get when you turn on hot water pipes running through an air conditioned basement!
Use solid core doors cut tight to the floors; there are other ways to get proper air return than undercutting doors by 1"!
Great separation between the bedrooms that your architect provided for will eliminate some of the biggest annoyances.
our builder, while excellent in many ways, is not keyed in to the different options to sound
Which makes him and his crew poor candidates for getting any of the crucial installation detailing right!
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