Well I don't have rj-45 to DB9 adapters at the moment, so I thought I would try it with serial cables...not one, but two. Here is what I got working!
[Sheevaplug] -> [USB A/mini cable] -> [USB Hub] -> [USB Cable] -> [Parallax USB-RS232] -> [Serial Cable] -> [Serial Cable] -> [CM11a Cable] -> [CM11a] -> [XTB-IIR]
but the other more preferred method didn't work:
[Sheevaplug] -> [USB A/mini cable] -> [USB Hub] -> [USB Cable] -> [Parallax USB-RS232] -> [CM11a Cable] -> [Coupler] -> [25' telephone cable] -> [CM11a] -> [XTB-IIR]
The serial cables are definitely more robust than the telephone cable.. I wonder if that has anything to do with it...
The whole point of doing this was so that I could plug the CM11a into the XTB-IIR to try an improve the dimming with a palm pad. Using a TM751 with palmpad dimming is quick, smooth, flawless. but with the w800usb and cm11a dimming takes forever...approx. 3 seconds in between each dim step.