I am sure that others will chime in with more info, but it sounds like your room is a candidate for acoustic treatment. This is re-inforced by your speakers sounding better in one room than this one. Hard surfaces (wood floors, sheetrock) bounce sound around and blur speaker imaging. Also, smaller rooms have more uneven bass response due to widely spaced room resonances (modes) that are a function of room dimensions.
There are remedies that may fix the problem, but unfortunately predicting the effects is inexact. You just have to try and see what works.
Many favor placing absorption panels on the side walls at the first reflection point. The first reflection point is the place where your main left, right, and center speakers' sound first bounces from the wall and arrives at your ears. Although a room will have many bounces, the first one tends to be the most noticeable to the ear. Absorbent panels mounted on the side walls are effective in reducing the amplitude of the bounce. They come in various colors and are usually 2' x 4' and 1", 2" or 4" thick. Pricing starts at around $30-40 for the thinner panels. These should improve your speaker's perceived imaging. I have had first reflection panels up for several years and they made a definate improvement in my room (12.5' x 20.5' x 8'). You select the place to put them by sitting in your favorite chair and have someone move a mirror around on the side walls. When you can see your speaker in the mirror, that is the place to put the absorption panels.
Treating a room for bass frequencies is different and often requires bass traps, which tend to be thicker (4"-7" and more) and are usually spaced away from the wall to increase the trap's efficiency. I am a recent convert to bass trapping and I can tell you that it makes an amazing difference in bass smoothness and transient response (kick drum, electric bass, etc.)
Anyway, that is a start. There are many on this forum much wiser than I on room acoustics and I am sure they will be happy to answer questions and offer advice.
