A lot of the DSS systems have both the RF and IR circuitry on the same boards. I know my dish network receiver is that way. I had the opposite problem it was an RF only receiver and I was frustrated because I wanted to use IR. Then a Phillips rep told me that it was too expensive to make unique boards for these receivers so they put both circuits in. In my case I had to go inside to jumper the IR circuit to make it work. I think this may be the case with your unit as you have a RF option. A faraday cap (technical name for a metal cap) placed over the RF input point may help. I would give a factory repair center a call to see what they can tell you.

Good luck
Bill
www.homeautomationnet.com