Foreverhifi has already said it: "the room is at least half of the equation." Of course, being in the business of designing rooms, we have believed this from the very beginning and feel that too many audiophiles are being robbed by their room. They could easily invest a small portion in the room and achieve likely the greatest upgrade they could ever imagine--and all future equipment upgrades would be far more significant. Your case is not alone, but at least you recognize the significance of the room.
I've said this in a few forum columns before, but I'll say it again. You have 2 options: DIY or hire a professional. Obviously, we would love for you to hire our group, but we would encourage DIY as well. The worst thing to do is ignore the rooom, which unfortunately is often the course of action.
As to your room, you do have some basic problems. First two of the dimensions are mulitples of each other and 14w having a 2nd mode close to the 3rd mode of 10h is another problem. You likely have some significant bass problems. Now, they may be masked to some degree by other issues, such as not enough high frequency absorption, so things seem somewhat balanced--except that mid range suck out. It's quite possible your midrange is the closest to being correct and it was both the high and low frequencies that were overly accentuated.
This is what makes acoustics somewhat complex and sometimes not that well understood. It's very easy for the ear to be deceived by 2 wrongs that are not making a right. For example, a room with lots of windows and losing bass energy will often be overcompensated by overdamping the high frequencies. Then the highs and lows are in relative balance, but it's still not optimized. I think your case may be the inverse of this.
Our website offers quite a lot of free advice. Please visit the listening room
. There are some issues discussed in this tutorial that may be useful to you. One thing I would strongly encourage is taking some basic measurements in the room, even if it's just a plot of frequency response and sound pressure locations, this can help you find some of the largest problems quickly. This doesn't replace taking more sophisticated measurements such as reverberation times, but it does help with many of the basic problems, and is always a good place to start.