While I'm an an advocate for stereo amplification, I refuse to totally dismiss the Bose PAS concept. I think it's viable if the sound is as good as some say, and the phase cancellation problem is not a fault of Bose but a naturally occuring acoustic phenomena. Bose isn't to blame... and nobody seems to think that two PAS units might not be a bad idea for keyboards. I'd love to run a real-time analyzer on a PAS and get some solid results to compare with other sound systems.

But the cost of two PAS units - yikes! So if you really want to go mono via PAS, here's a phase adjustment tool that runs about $375 reportedly that might solve the phase problem: http://www.littlelabs.com/ibpjr.html

I don't know for sure that the IBP Junior Analog Phase Alignment Tool would work but it seems like a solid idea. This could be useful in the studio anyway. So it may be possible to start with a single PAS unit and a phase adjustment tool and then save for an eventual second PAS unit, if you are Bose-motivated.