Ted,

Just to give you and everyone else an update. I just got off the phone with Xantech's technical support and they said a 10k ohm resistor should do the trick! Thats 10x the resistance recommended for the HR21 boxes which is why none of the combinations I tried last night worked.

I'll swing by RadioShack tonight on my way home and pick some up and give them a try tonight. For 99 cents you may want to go ahead and try too! :) Good luck.