There were two components to solving the problem. First, the 3000's mono (L/R)output is a psuedo mono--not a true mono output. Consequently the sound is not really a combination of the two channels. I combined the two outputs in the by running both outputs to two channels of the PAS system with identical settings--what a difference.
While the piano sound was still not as good as it would have sounded in full stereo, it was OK. The next step was to select the GM Grand Piano, then tune, tweak and perfect the sound so it sounded even better than the Live Grand Piano sound. This was done using the keyboard's onboard sound creator, which does an excellent job. The sound was then saved to the user area, which can be selected just as easily as any other sound.
The one thing I highly recommend is tuning the 3000's Master EQ to the sound system you are using. Every system is different and must be treated accordingly. I use different settings for the PAS than I use for the Logitech Z-5500, and a completely different setting for the Barbaettas. No two systems are alike, and this often applies to identical PA systems.
Spend some time tuning the EQs with the system you are working with. Do it in a large room, and record a midi file using the 3000, one that used all the instruments you would normally use. Then play that midi file while you walk around the room, make some EQ changes on the Master EQ, and walk around the room again. It takes time, but after a few trys you'll find the sound you'll like. Then, save the settings, write them down on a piece of paper to be safe, then you'll enjoy that next gig a lot more.
Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)