Scott, I know phase cancellation happens to all sounds, but I am sure Yamaha's way of producing the stereo samples is the problem...I think it may not be a true stereo sample as found on Roland products..I think it is designed with it's own effects with in the Yamaha keyboard...that when reduced to mono, loses the stereo image...I have played stereo sample sounds from Roland without the problem we see in Yamaha...I have found zero phase cancellation with the sample...We would be more incline to find it with a random effects, used to simulate a stereo sound...I would be curious to know if I am right...Yamaha is not using true stereo samples..only mimicking a stereo sound with it's effects..