Building a house

Lots of helpful advice. I’m in a similar position so appreciate the expertise. My dedicated room will be a bonus room above the garage so little worry about soundproofing other than a sturdy door. My main concern is trying to find the right mix of design and build materials so that the space is neither too dead or reflective. The room is 21x15 with 5 foot knee walks going up to a 9 foot peak. There will be a shed dormer on one of the long walls and the system will be on a short (exterior) wall. I will do a wall mount shelf for the table screwed into a boxed in section of the wall between the 2x4 studs. I did this at our prior home and it worked well. I’d appreciate thoughts/opinions on the room dimensions and use of building materials and room treatments that will diminish first reflections and bass nodes/issues—please PM me if your suggestions do not also apply to the OP.

All super helpful comments here. I'm in the final design phase for my 17 X 23 with peaked ceiling bonus room over the garage and need to specify build specs for floor, interior/exterior walls, and ceiling. Here is what I am thinking:

• 5/8" drywall screwed and green glued over studs (2X6 exterior and 2X4 interior) with mass loaded vinyl sheets and rockwool sound batts within the cavities of interior walls (regular insulation on the exterior walls).
• 5/8" Quiet Rock on the front wall behind the speakers to create dead end/live end arrangement.

Not sure what to do with the floor joists and flooring could use some help here since this will be the most problamatic surface--brace the joists and add a layer of mass loaded vinyl beneath the plywood flooring? The floor cavities will be filled with regular insulation since the unheated garage is below.

The goal is less about sound insulation and more about making the room sound good--reducing wall and floor shudder, etc.

Thanks!