OK, now I get it, thanks for the help.

I have done hours of research on many forums, especially the Bose forums where the issue of stereo piano sounds through an L1 has been discussed to death. I have also conducted hours of my own tests with my CP33 Yamaha through my L1 Compact and have just finished my first gig.

The issue is that the sound you get from a stereo piano patch when listening on phones or via two monitors is not really a piano!! It's a "stereo piano" which doesn't exist in the real world. Other acoustic instruments are mono and their synth sounds are mono so when you put them through a Bose they sound great. The keyboard manufacturers have concentrated their efforts on creating stereo piano patches which, when you combine to mono, have all sorts of phase cancellation issues which is why they never sound as good through a single mono PA like the Bose. Running through left and right speakers restores the "stereo piano" sound but then we get into the issue of how many of the audience are positioned to hear the stereo etc. With their "stereo pianos" the manufactures have created unrealistic expectations among first time performers like me!

The only way to avoid degradation of the sound quality is to use a mono piano patch - if your keyboard has one and mine luckily has one. No matter how you try connecting from keyboard to mixer to Bose using a stereo piano sound, the quality always suffers. This is true even if you use the L/mono keyboard out which seems to just do an internal stereo to mono conversion. At first I ignored the mono piano patch because it didn't sound as good as the stereo patches but then the penny dropped - The reason it wasn't as impressive was because I was hearing a real piano, not the artificial sound of a "stereo piano" Most importantly it sounds the same on phones or through the Bose - why wouldn't it, it's a real piano.

The final clincher was getting someone to work some tests with me at the gig location and the gig itself. Everyone thought the mono piano sound was great and better than any of the stereo to mono sounds. Now I have got the sound of a stereo piano out of my head I am at peace with the world.

One final comment. I was lucky when I bought the Bose that my keyboard already had a mono piano. It certainly wasn't on my list of priorities when I bought it. Before I recommend Bose as a keyboard PA I will point out that they may be disapppointed with the piano sound unless their keyboard has a mono piano.

Tony