Hi,
before giving it away, I tried an older surround sound system, with my s950. The bass speaker was plugged directly into the keyboard out, but the L/R speakers were wireless ( Bluetooth? I think, Not sure) either way totally useless for live play, the latency was really noticeable. I thought maybe I was doing something wrong, and gave up.
Sort of good to know it may not have been me after all, either way, my son got himself a surround sound setup.