I havent used it, but a studio designer I've done carpentry for isn't convinced it's worth the extra $$ yet.

Well-detailed and properly installed RC with double 5/8's is pretty good; is the rest of your design (doors, windows, HVAC, floors, etc) up to the same isolation level as the drywall? If not, I wouldn't spend the money.

Frank

Try building a wall with 2 outside sheets of sheetrock and filling the 2" internal gap with sand. I can assure you that this will absorb loud bass frequencies, but bass traps also help. It's a hassle and expensive, but it is infallible.