Having owned large clubs, I would suggest something with a mono switch. Unless you plan to paint only in 1 specific spot nothing will ever sound right, especially with all of the room reflections. Bass is going to be boomy and highs will probably sound bright at higher levels. Also, your canvas is going to act like a sound shield right in front of you.
I'd start with something like the Sherwood mentioned above (it should have a mono switch). For speakers, consider 4, not 2 if you are going to go mono. Sound will be much more even. Most older receivers will happily drive 2 pair of speakers. I'd lean towards smaller monitors since bass should be a problem.
Finally, store your canvasses in the corners to act as bass traps?
I'd start with something like the Sherwood mentioned above (it should have a mono switch). For speakers, consider 4, not 2 if you are going to go mono. Sound will be much more even. Most older receivers will happily drive 2 pair of speakers. I'd lean towards smaller monitors since bass should be a problem.
Finally, store your canvasses in the corners to act as bass traps?