Figured I'd make a new thread, rather than update my original one, which was more of a rant.
So here's how I did it, and I'm sure you can do this with ANY digital piano.
What you'll need:
1 continuous (half-damper) sustain pedal
2 switch pedals
1 MIDI Solutions Pedal Controller
1 MIDI Solutions Dual Footswitch Controller
3 or 4 MIDI cables
Optional MIDI-USB interface
Just see the diagram for connections.
You'll want to turn off your piano's "local control" so that the tone generator responds only to MIDI, not the keys directly... unless you want an echo effect. LOL
For sostenuto and una corda, pretty much any piano-style switch pedal will work fine. For the sustain pedal, stay away from reverse polarity pedals, like Yamaha's FC3. While the MIDI Solutions Pedal Controller can be programmed to function in reverse, the feel gets messed up. I'm using Roland's DP10.
I'm also using a MIDI-USB interface that features a thru switch, so I can use this setup to record MIDI, but also play the piano without turning on the computer.
The MIDI Solutions products are freaking expensive--$200 for the Dual Footswitch Controller and $125 for the Pedal Controller. But the only other alternative, the CME GPP3 pedal, is a seriously flawed unit, with dismal tech support. John at MIDI Solutions is on the ball and stands behind his products. It's still cheaper than getting a new digital piano (at least one that I like better than what I have).
So if you love your current digital (like me), but it doesn't "support" full 3-pedal functionality, try this. Just double check the MIDI implementation chart in your manual to make sure your DP recognizes MIDI Control Change #'s 64, 66 and 67 (sustain, sostenuto and una corda).