Jason,
The MX-850 replaces the MX-700 (IR signal) and the MX-800 (RF signal). IR means line of sight, RF (radio frequency) means "no matter where you point it". Rf comes in handy when you have equipment out of sight or enclosed.
The way they have done it is to enable either signal to be transmited by a setting in the remote. If you plan to use the RF function, you will need to order the RF Base Station. Also, be sure your equipment is both IR and RF capable. Most everything handles IR; RF is a little more scarce.
I believe room-to-room would be OK, but upstairs downstairs might strain the RF capability. Let me suggest you give Mike a call at Surf Remote Control. He is an expert and very helpful to boot.
