Hey Dick...did you find the time to check out the Sennheiser system yet? I'm interested to find out what people are using ..
I did have a chance to experience the Sennheiser rig with a few sets of headphones. It was really excellent. I tried 7506's, HD 280's and these:
http://www.sweetwater.com/store/detail/HD25mk2/The HD-25's were definitely the best and have a "one-ear" configuration where you can rotate the left ear-piece 90 degrees and listen to the ambient sound. So it looks like the bill for a complete rig is the cost of the G3 wireless and about another $250.00 for the 'phones I liked.
For that money I could buy another small digital "MixPad"...