Tomlinmgt is right. If the bass is already boomy, corner-placement will likely accentuate it. My bad on that.
One thing I recently learned is the importance of strong, balanced electrical current, not to mention what it can do to your system's response when you DON'T have strong, balanced current. Do your overhead lights and lamp lighting get dimmer during heavy usage hours where people in your area are using more electricity on any given day? If so, that could be part of your problem. As someone explained to me (and I discovered was the case in my situation), if you're at or near the end of a long powerline run, it can cause those kinds of symptoms (dimming of lights at busy neighborhood-usage hours), which can wreak havoc on your system's response, especially the bass and dynamics.
If that's the case for you, you may want to look into an uninterruptible power supply (or simply UPS) with automatic voltage regulation. I'm running tube gear, so I wanted to deal with my problem once and for all, so I bought a professional-grade UPS/AVR with line-conditioning off Fleabay, and it did wonders for my system. Flattened the response out, made the bass quicker, stronger, and more-dynamic, and improved clarity and extension. And the line filtering dramatically-reduced my noise floor. Best $120 I ever spent.
Not saying that's the cause of the problems in your situation, but I figured it couldn't hurt to mention it just in case.