I play with a Korg Triton ES and when I go through a MONO amplification system, my samples sound like crap. Also, when I use my Roland VK8M Drawbar module with it's stereo Leslie Effect through a MONO amp IT sounds like utter crap. The leslie sounds more like a vibrato.

I don't think this problem is a Yamaha only problem. That's why I play through a stereo amplification system exclusively. I'm very curious to see what my equipment sounds like through a Bose PAS to see if it handles summed stereo any better.