Re: What to do?
Using 2 layers of drywall of different thickness (1/4" and 3/8' different thickness have different resonance characteristics.) with some other material of choice (carpeting or carpet padding, etc.) sandwiched between them will both reduce/remove sound reflections and soundproof the room.
Anthem, Conrad Johnson, Dish Network/JVC, Dynaudio, Infinity, Integra, JL Audio, Klipsch, Magnepan, Marantz, Martin Logan, Onkyo, Oppo, Outlaw Audio, Panasonic, Paradigm, REL, Sumiko, SVSound, and Toshiba are the brands equipment I currently use. I have owned/used and tested equipment made by just about any manufacturer you can name.