I have been happy with the piano patch sound from my Yamaha keyboard ever since I bought a second Compact and run them in stereo. I then decided to upgrade my cheap Behringer mixer to a A&H ZED-10FX and the quality disappeared!! A&H told me that with the "listen" button pressed, which allows you to operate the phone volume independently from the main mix volume, the signal from separate channels is summed to mono!!!! With the "listen" button off, the stereo and the quality is maintained. I don't know why they would design things this way and there is no mention of it in the manual

This is further evidence that equipment manufacturers don't appreciate the effect of summing stereo piano patches to mono.

Tony