You might want to check with ARC support. I believe the device required a stereo signal to work at all.
Experience with Audio Research SDP-1
Looking for anyone with experience, pro or con, with using the Audio Research SDP-1. The SDP-1 was Audio Research's attempt at pseudo-surround sound. It synthesized rear and center surround channels and was available in the mid to late 90's. I borrowed one from a fellow audiophile and have had mixed results. When the source material is right it sounds good, but with some material the rear surrounds (I'm not using the center channel) have what sounds like a high distortion level. This is especially noticeable when playing a mono source. While the sound is intriguing, the occasional distortion and added complexity to the system makes me cringe!