I would highly recommended at least some acoustical treatments in your room. At the very least, add some treatments to tame the first order reflections. I noticed a big difference in the clarity and depth when I had treatments to my theater. Keeler Theatre
I think a mistake many people make when it comes to this is over treating their room. The goal is not to make it a dead space. If you've ever been in an anechoic chamber or in an area where there is no natural reverberation you'll recognize how uncomfortable it is. We live in a world of ambience, and when you take that away things just aren't right. The goal in treating a room is to selectively damp and diffuse sound.
First order reflections are the biggest culprit. They're delayed just enough from the primary signal that they smear the sound. Finding them is easy - just have somebody run a mirror along the side walls while you sit in your normal listening position. When you see your speaker reflected that's a first order point. Angle of incidence = angle of refraction (just like playing pool). The same is true for the ceiling. In addition it pays off to absorb reflections behind the LCR speakers.
Diffusion is effective above, beside, and behind you. Diffuser panels look like mini citiscapes. Their purpose is to reflect sound in a natural random sphere. This helps with creating an ambient field that goes beyond the room's boundaries.
Combined in strategic locations this combination along with the room's natural reflectivity will make a huge impact for relatively little dollars. If you really need to keep the costs down stick with the first order points to start. Acoustic research gets very, very in depth when modeling of surfaces and such is concerned but at that point you need to seek professional help.