Advice on system and speaker placement-B&W

My system is the following:
B&W N804 speakers
Musical Fidelity a3cr pre
Rotel 1080 Amp (200 watts/channel)
Cary 303-200 CD
Harmonic Tech Truthlink Interconnects
Tara Labs Prime 100 Speaker Cables
System running for three years now and fully broken in

My room is 20 ft wide, 35 foot long and 15ft high, along the right 35' section, there are several large openings into other rooms, along the left side of the 35' opening there is a large opening into the entryway. Speakers are 10 inches off the 20 foot wall and 10 feet apart (I can't move the speakers out further into the room).

My system sounds wonderful on well recorded rock, jazz and classical, but many CDs sound thin and uninvolving, with too much highs. Does anyone have any advice as to how to make my system sound better for the other 65% of my recordings? I have started other threads on this topic, but without the whole story on my room setup. I am skeptical of expensive changes to amp/preamp because my system sounds just great on 35% of my recordings. I could use a sub, i could look at new speakers (i like a rich full sound but with dynamics), or maybe an extra CD player (that is easier on the recordings-but not sure if this would be enough to solve the problem). I know this is a complicated question, but there seem to be many of experienced folks out there. Anyone have a simliar situation or setup and advice? Any help would be appreciated.