Unless your room is very sparsely furnished, I wouldn't invest too much in wall treatments. Normal stuff like carpeting, bookcases, curtains, etc., actually do a pretty good job of taming acoustic problems. Acoustic treatments is a complex endeavor to do right, and if you don't do it it, its just throwing away money. From your description of your room, it doesn't sound like you really need it. I would just get a decent pair of floor standing speakers and a simple amp or AVR. Take some care in its placement and positioning, that will make a bigger difference than acoustic treatments. Do a little bit of research for good speaker for optimal speaker placement.