They'll play on the 550 if you remove the OTS settings using Jorgen Sorensen's noots program. If you don't remove the OTS, they'll lock up the keyboard and you'll have to reboot.

Enjoy,

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.)