"I am not even sure I need to fill up a large room. I just want to be able to turn it up occasionally so it plays into the kitchen."
The further you are away from the speakers, the more you must turn it up for a perceived volume. Also, speaker sensitivity determines power necessary for a certain volume. The highest sensitivity speaker in this post is 99db and the lowest is 84db. For the same volume, the 84db speaker will need 30x more power than the 99db speaker. As I previously stated, bass distortion increases when a speaker is driven to its maximum, and this will likely happen when trying to increase volume over a distance with a low sensitivity speaker.
As far as needing to turn up the treble, speaker placement in the room could cause this. Are your current speakers on a stand, table, floor, or in a bookcase? If in a bookcase, pushed back or pulled forward? If not in a bookcase, how close to back and side walls? In a corner?