speaker placement in a tough room, please help.

Dave: This is not an uncommon occurance. The reason has to do with the reverberation times of a large vs small room. In a small room the reverberation times are short and they actually add to the spaciousness of the image because psychoacoustically we hear these short reverberation times as part of the original signal. In a large room the reverberation times can be too long and they are perceived as a seperate signal disconnected from the original signal. The result is image smearing. One other thing that happens in a small room is pressurization of lower bass notes. You need about 28 feet to have a half wavelength of 20Hz. At whatever your maxium dimension is (diagonal is accepted) this will accomodate the maximum 1/2 wavelength. Any frequency lower than this will pressurize the room. You can get a bass gain from this (this is how car audio works in low frequencies). It is not as natural sounding, but if it occurs where the speakers naturally roll off it can create improved bass response. In general, large rooms can work better, but they have to be properly attenuated so that reverberation times at anything less than a 60dB drop are kept to a minimum. The biggest problem I see with your room is that 2 dimensions are very close to being the same and the ceiling height crosses through both of these dimensions as well. You are likely to have a boost around 50-55 Hz. Low frequencies like this are difficult to deal with using passive devices and usually require active equalization. If you feel the bass is not correct I would suggest you measure the room acoustically and see what the response is.

Rives and Kana813, thanks for the responses. I always prefer to listen in a dark room regardless of size, since I agree with you that the distractions are absent and the music seems to bloom more.
Incidentally, the Hales Sig's 2 have little bass info below about 50Hz anyway. They utilize two 6" drivers for mids and lows. According to Paul Hales they were ample in the bass,however, most audiophiles including myself disagreed. IMHO only large drivers,i.e. 10"+ are able to really move any substanial air in order to reproduce the lowest frequencies. I know theoretically two 6" drivers equals one 12", but and this is a BIG but, I have never heard two 6's that could reproduce the bottom octave like one good 12".
I'll post on the results as soon as I have moved the speakers into the room and got them set up. Thanks again.

As to the driver question it's really the area of the driver that determines how much air can be moved. This alone does not determine the roll off frequency, but two 6 inch drivers can move as much air as one 10 inch driver. In addition a 6 inch driver has less momentum than a 10 inch driver and thus is easier to control. The result is typically two 6 inch drivers will deliver cleaner sounding bass notes than a single 10 inch driver.