10-11-15: Zd542
You can't fix a high frequency timber problem with room acoustics. I've tried to do this many times. The directionality of the high frequencies just doesn't allow for it. There's a direct line of sight between the ear and the tweeter, and the only way to make any progress, is to change the sound coming out of the drivers themselves.
True, but the only way to manage expectations, is to demo equipment before you buy it. Otherwise, its just guessing and hoping for the best.
Room acoustics will address most frequencies in the spectrum from high to low. High frequencies are easier to address whereas low frequencies are more difficult as mass/volume is required for absorption. Piercing highs or a bright sound is mainly due to less-than-ideal acoustics of the room (other than bright speakers) caused by reflection of sound waves from hard surfaces. Have you used aftermarket room acoustic products before? I used to have a dedicated room and have tried several acoustic products all over the room (I prefer diffusers more than absorbers, though a combination usually works wonders.)
Demoing equipment in-store and listening to the same system at home will likely(or should I say mostly) produce different results. That is the reason I have mentioned there isn't a 100% guarantee that one will be happy with the results even after a demo session in-store, as the results at home may turn out to be completely different due to the setup of the speakers/equipment and room acoustics. However, it is still a better option than doing without an audition.