Connect headset to Contour 2 remote box.

I have a Contour 2 DVR w/remote box for another TV. I also have two wireless headsets that connect with a red & white RCA plug to audio outputs. Easy enough to connect to the DVR, but not the small remote box. This box has only a coax in, coax out, and hdmi out to the tv. How can I hook the headset to this?