Tweaks when building a listening room?

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.

Some bass problems can be predicted from the room's dimensions; or, if you have not started the building process, the dimensions could be changed to those that minimize bass problems. Built-in bass traps designed by an acoustics engineer can be more effective and aesthetically more acceptable than after market units.

Thanks everyone for the input. I used every one's suggestions in some way or another. I'll give an update when the room is complete.
Thanks again,
Marc

Angle the ceiling?

Instead of 2 x 1/2 inch drywall, I suggest 2 x 5/8 inch. I also strongly suggest gluing the drywall to the studs & between the layers,in addition to screwing. Tape and mud the 1st layer before applying the second on an offset of course. The difference is not subtle and the cost is not prohibitive. Install soundproofing, tape and a trim piece along the gap where the drywall does not touch the floor. I would want a spare 20 amp line as well as normal 15 amp outlets per code.
I envy you-have fun.