Double-rock the drywall and use the very best sound insulation you can afford between the studs. There's a very dense specialized batting for sound, or blown-in is excellent as well. If you plan on running any systems in other rooms you may consider running some wires before the walls are buttoned up. Cat-5, speaker wire, and a set of coaxial wires would all be useful in running an extension system. I also did two dedicated 20 amp circuits and kind of wish I'd done a third.
Good luck!
Good luck!