I never did play a keyboard that had a modulation whell but I would guess all it does is... it induce a vibrato and you can control the speed of it ??? Thinking of it now...when the warranty will be expired on my WK-7600, I will just open it up and replace the push button switch and install and on-off switch of the same size that will fit in the same opening. It will be totally clean and practical. As for an after-market moduation wheel installed outside the WK-7600 keyboard...it's just the same problem as the outside MIDI-in MIDI-out unit you can buy. It's expensive ( $100.) One would guess it would have cost a lot less than this for Casio to include it in the keyboard itself. Last, in the manual, they say you can get rid of the vibrato (on the modulation button) and replace it by a DSP. O.K. but...since the vibrato itself isn't a DSP. how after replacing it could you put it back there??? Maybe, it automatically returns there as the default once you shut down and you power the keyboard again?