Edumund you are so right as I have since found out! I bought the MX350 thinking by changing the channel # to something other than "0", it would no longer communicate with the MRF100 (which I thought was permanently set to ONLY receive channel "0" even though you can't change its channels). I now see it actually receives ALL of the RF channels from the MX350 and your solution is the only correct solution.

So back goes the RF-S200 and I'll just get another MX350/MRF250.

Thanks again.