To follow up -- It seems that all is well :-). In setting up the RF I had set both the menu device and the IR codes "device" to RF. Resetting the menu page to IR cleared up all sorts of problems. I suspect that the infamous "toggle bit" problem was cropping up as I guess I was sending duplicate commands - causing all sorts of confusion in the XM receiver. I still don't understand why this was only a problem with RF, as IR always worked perfectly.

Much appreciation to Lowpro for the assistance!!

Craig