Tweaks when building a listening room?

I recently finished a dedicated 2 channel room and used double 1/2 inch drywall and all walls were double insulated before the drywall went up. I too brought in two 20 amp circuits and two 15 amp circuits for power.

The best tweaks you'll make will be after the room is finished using room acoustic panels.

If you are considering a dedicated circuit: Use(as least) two runs(keep 12" separation between the two) of 10-2 Romex(equiv of 4Ga), and(minimum) hospital grade outlets(ie:http://cgi.ebay.com/Leviton-Ivory-HOSPITAL-Receptacle-Outlet-20A-8300-I_W0QQitemZ250202544990QQihZ015QQcategoryZ41985QQcmdZViewItem). Also- Consider Auralex, or some of the substitutes available on eBay, to deal with the reflections inevitable in a listening room. Click on topics: (http://www.asc-hifi.com/acoustic_basics.htm) (http://shop.ebay.com/items/__acoustic-foam_W0QQ_nkwZacousticQ20foamQ20QQ_cqrZtrueQQ_nkwuscZcousticQQ_nkwuscZfoamQQ_trksidZm38)

Thick carpet, bookcases, thick drapes over windows, sliding doors, and upholstered furniture will all contribute to improved bass extension, soundstage, and overall fidelity. Avoid openings to other rooms without doors. Keep the doors closed to keep the sound in. Enjoy !!

Prior to my listening room remodel, I contacted Cryo-Nebraska who in turn locally purchased 500' of 12 gauge and 14 gauge romex at their local Home Depot, double-cryo-treated it and shipped to me which was then installed for my 4 dedicated lines.

A few other tidbits include premium wall-to-wall carpet with premium pad, few windows, no hard-surfaced furniture including tables and leather, and recessed lighting.

These few basics, good room dimensions, and proper speaker placement should be all you need for a superior room.

For everybody else in the house and neighborhood I suggest insulating all walls.

-IMO

Is this all new construction?

You can 'stagger' the studs. This, with proper insulation will help decouple this room from the one next to it. In this way, the sheetrock in each room will NOT be back-to-back on the same stud.
You can also weave some Very Heavy, acoustically dense materials between the studs to help reduce sound transmission.

Built ins? Book shelves work and are a good design element, too. Stuff 'em with your paperback collection!
I would also use an EXTERIOR=solid core, 36" door as an Interior door.
Is it possible to install a barrier in the attic to prevent sound from going 'over the top'?
Prewire for as many speakers as you think you'll ever need.
Use 'econotube' flexible conduit so you can later pull or replace wire.
Double sheet rock? Not all 4 walls. Maybe, the wall next to the existing construction and 1 adjoining wall.
Make SURE you get Low-E thermopane glass, too.