Tony, (or anybone else using 4 or 5.1 surround for keyboard amplification)

When you are playing your keys thru the Z-5500s, you are hearing a surroun-sound effect, right?
You hear an enhanced quality of sound, MORE than just the standard quality of left/right stereo. Is that right?
If so, does that triangular area commonly referred to as the 'sweet zone' or sweet area increase/open up because of the 4.1 / 5.1 multi-channel configuration?
-- or --
do you guys just get the stereo quality, but coming out of more speakers?