To the OP: Do you use any other sources to watch TV (e.g., Blu-ray) other than the cable box/DVR?
Nick_sr's solution is the most complete. Any surround processor that supports Dolby Digital surround and has a Toslink input will solve your problem. And if you add other video sources such as Blu-ray, you can use the Blu-ray's Toslink output and connect it to the surround processor as well. And as Nick_sr said, configure the surround processor to downmix everything to 2-channel, feed your TAD the analog 2-channel output and you're good to go.
Even though the DVR has an HDMI output, it almost certainly also has an analog stereo output. You can run the HDMI cable to your TV for best picture and the analog stereo output to your TAD for best sound quality. In this case turn your TV's audio off. And if you have or plan to add Blu-ray, every Blu-ray player I've ever seen also has an analog stereo output. In these cases (DVR and Blu-ray) the stereo downmix has already been done before it goes to the stereo analog outputs.
Nick_sr's solution is the most complete. Any surround processor that supports Dolby Digital surround and has a Toslink input will solve your problem. And if you add other video sources such as Blu-ray, you can use the Blu-ray's Toslink output and connect it to the surround processor as well. And as Nick_sr said, configure the surround processor to downmix everything to 2-channel, feed your TAD the analog 2-channel output and you're good to go.
Even though the DVR has an HDMI output, it almost certainly also has an analog stereo output. You can run the HDMI cable to your TV for best picture and the analog stereo output to your TAD for best sound quality. In this case turn your TV's audio off. And if you have or plan to add Blu-ray, every Blu-ray player I've ever seen also has an analog stereo output. In these cases (DVR and Blu-ray) the stereo downmix has already been done before it goes to the stereo analog outputs.