help with a sometimes boomy sounding room..

Well, here's my low down.

my listening room size: 10'6" wide x 13'length x 7'2" Hi.

my gear: Classe CA-201 w/ reference XLO power cord,
Classe CP-60 w/ Classe reference power cord, MIT Z center w/ Z cord, Sony SCD-1 w/ cardas gold reference power cord,
Monitor Audio GR(gold reference)'20's
MIT MI-350 reference balanced 1 meter from SCD-1 to CP-60,
transparent balanced musinlink-plus 1 meter from CP-60 to CA-201, 10' transparent bi-wire musiclink-plus speaker cables.
I have acoustic treatments on (both) back 10'6" walls , also have treatment behind listening chair at ear level, treatments centered on 13' walls, floor is carpeted with 3/4" padding.

The boomyness on seems to exist during certain songs with heavy bass tracks..., have not had any boomyness when playing SACD's...

The monitor audio's have a great soundstage, good depth and image great.

The speakers are 33.5" off the back wall and 16".5" off the side walls.

OK, tha't's it. Any thoughts.....for improvement?

thank you so much for the long read!
if your room is really 10x13x7 it's just too small to not give boomy bass.
I recommend the following: get the speakers further into the room and sit closer to them, turn the volume down, and in the last resort, try simpler cables/different music.
or move them into a bigger room ;)
there's some info on speaker placement on the cardas website....
The room is indeed rather small, but there are some tricks that can help. Firstly, acoustic treatments will probably not help the bass, unless they are very large "bass traps". What will help, as Tacs has suggested, is speaker placement and listener placement. The best rule I have found to bass response is PRIME NUMBERS, kind of. Every pertinent dimension should be as unrelated to another as possible. I see for example, that your speakers are almost exactly twice as far from the back was as they are from the side wall. This even multiple means that specific frequencies will be doubly mangled by the two dimensions. But if the two distances were less related, each dimension would mangle a slightly different frequency, hopefully evening out to some extent.

Lastly, boomy bass in a cd player can sometimes be reduced by using Cones under the player, or some other form of vibration tweaking that couples the player more tightly to the rack.
The small room is definitely the main culprit. Audiofile9 also points out the speaker placement could be optimized a bit and possibly reduce the problem to some degree. In a small room, low frequencies are not supported by the room dimensions, as there is not enough space for 1/2 wavelength to travel within the room. Instead, the room is pressurized, much like what happens in a car. When rooms are pressurized in this fashion there can really be some significant problems, most revolve around pressure points in the room and then peaks of certain frequencies at certain points. I'm not speaking solely of room resonant modes here, but that no doubt is also occurring. The first thing you should do is measure the frequency response of the room using a test CD and an SPL meter. There are better ways of measuring the room, but this method is very inexpensive and will give you an idea as to what frequencies are giving you the biggest problem. Undoubtly, the room resonant modes are giving the greatest problems, but with small rooms like this you will likely find some other frequencies (or bands of frequencies) that are giving some problems as well. After you find what your current response is, you at least have a starting point. Then you can more objectively evaluate changes, such as speaker placement, listener position, and room treatment. Believe me, it's very difficult to do this solely by ear. By ear works very well for the final tweaking, but can be very frustrating in the interium because there are so many interactions occurring. For example, you may do something that compensates for one particular problem and it sounds better for some music, but then can actually sound worse for other music.
I'm going to back up the speaker/listening chair position theory. I too have a very small room (9x12x10) and have found that listening in a near field position helps eliminate many room anomilies. A good starting point is the "rule of thirds" in which the speakers are 1/3 into the room and the listening position is 1/3 into the room. Good luck.
Here's my constant recommendation for this and many other room acoustics issues: buy F. Alton Everest's "Sound Studio Construction on a Budget" or his "Master Handbook of Acoustics, 4th Edition". You'll learn how to analyze your room quantitatively, and learn what you can do about room resonant modes that give you boomy bass. If you read most of it, you'll learn how to deal with problems arising above 300 Hz too, with absorption and diffusion.
Sounds like the bass drivers on your speakers are unable to handle lower frequencies. Use an amplified sub-woofer and carefully "dial-in" the bass response using a CD that has a lot of bass cords or scales. The object is to get a continuation of bass response where the speakers stop responding, i.e., a natural unbroken progression of bass notes down the scale.

The sub-woofer should be connected directly to the pre-amp. Hopefully your pre-amp has two sets of analog outputs. If not, you need to try a pre-amp that does.

From your description it sounds as though you are sitting 6' from the speakers, is that correct? Is that the alignment the manufacturer suggests?
I had a similar problem in a similar room. I didn't want to give up my full range speakers for smaller monitors because I wanted to have a stronger bottom than monitors offered. I bought large ASC cube traps for the back corners, but they made little noticeable difference.Finally I bought the Accuphase DG-28 eq, and that corrected the problem completely. I had real bass, without it overtaking the rest of the spectrum. The Tact works equally well on standing wave problems.
Good Luck
You don't specify what type of acoustic treatment you have on the back walls, but as Audiofile9 points out, only bass traps will address the problem you describe. Most surface treatments only tame reflections above 300 Hz or so. I use ASC Tower Traps and am very satisfied with the improvement they made in a small room....much cleaner, more articulate bass.