SOLVED
Thanks to Bill Brandom's suggestion I've found what was causing the playback issue.
Somehow the Sonos player was swamping right and left channels on its equalizer setting or iTunes may have changed the setting. All of this happened when I updated my PCs to Win 8.1 and my server to WHS 2011. I've had nothing but problems with other equipment and programs since going to the new Microsoft operating systems so I should have guessed that it also effected the Sonos and iTunes programs. We may also find others who use PCs and/or other equipment to send songs to their Disklaviers are also running into this problem as more folks upgrade their software.
It's working great again and the beauty of this setup is I can have all of my favorite Smart Pianosoft music on my server without having to handle the often delicate and cumbersome CDs.
Go Disklavier!!