One more comment. The things I suggested above can also be used in the 20x28 room, so the expense would not be wasted.
A couple recordings I can suggest (available in Hi-Res at HD Tracks):
Meloday Gardot - Lisboa (from album The Absence). The chime and bell instruments in this song are excellent for listening to imaging/depth. This song also has excellent deep/strong bass. Vocals and recording on this entire album is just outstanding.
Diana Krall - In My Life (from album Wallflower). I used this song to show how much midrange blare/ringing I have in a system. It’s very easy to determine this when you can hear the blare/ringing/boominess in her voice on this particular track. This really lead me to determine I had standing waves being reflected in the corners. My speakers are stuck back in the front corners as well (due to room size limitations). Other elements that can help clean up this midrange blare/ringing are improved power cords, interconnects and fuses. Some speakers are more sensitive to others. I have B&W Diamonds, which have a VERY strong midrange, so this problem is more apparent.