I think I'm going to have to add this to my to-do list :D
http://www.ooishoo.org/ym2151shield (http://www.ooishoo.org/ym2151shield)
Haha ! Very very fun project ! ;D
Long time I want to build such thing... But never found the time to !
If you are interesting into YMs fun projects, here is a site with similars implementations for many yamaha FM synth (YM2151 included) : http://sue.niko.to/ps98/ (http://sue.niko.to/ps98/)
Schematics are for hooking with a Cypress EZ-USB FX2, but can easily be adapted to arduino.
wow awesome!