mono versus stereo ampflication

I have a large room (22X38, eight foot walls to 10 foot peaked ceiling) I listen mostly to classical and 60's rock at volumes of what a normal symphony attains. I listen near field at about 10 feet from speakers but also like to load the room.

Thank you for all your responses. To clarify further my speakers are rated 20 watts to 500 watts. I am considering the Pass Labs INT 150 versus their XA 60.5 monoblocks, which I know complicates things because it is an integrated amp. It is appealing to me becuase it has the new XA.5 technologies in it as best I understand. But the downside is that I really like my current AH preamp. I am not yet aware of a high quality stereo amp in the price range mentioned new or used that I should be considering.
I am further uncertain about wattage - as best I understand if the 60 class A will drive the speakers loudly enough, then is it necessarily true that other things being equal that 200 watts class A would be better sounding?

Responding to comments and questions:
Rleff - I am planning to use my Audio Horizons 2.0nB preamp in balanced mode and connect to Von Schweikert VR4Sr's by biwiring.

Peterayer - I heard the XA100.5's in a friends system a few weeks ago and they started this search for better amplification. They sounded (as part a a great system and room) incredible. Congratulations on your choice. I am trying to approach that sound a a bit lower the price. Best I understand from reviews the INT 150 was designed to function much like the XA.5's for the first watts

Grannyring - thank for recommending the TRL's. I will check them out. Have you heard them compared to Pass?

almarg - Great suggestion - I have been concerned with energy use,cost and heat with the class A, but am hearing from reviews that the XA.5 are a very significant improvement. Does make sense to see if I can to hear the difference in my system.

I thank everyone else as well for their input.

Just for closure feedback. Thank you everyone for your comments they were very helpful. I decided to go with mono's, the Nuforce Reference 9V2SE's which seemed at a great price used. Had them a week and so far so excellent. I am getting great controlled, tuneful bass, good balance accross the spectrum and sparkling highs. So I am happy to now sit back and enjoy the music. Well - plan to do a little tweak in terms of vibration control and perhaps power conditioning. Happy Holidays
Joe