Having similar issues with HR20 and no sound on SD channels. Started after a reboot yesterday to try to fix my other issue, which is that my HDMI out -> HDMI to DVI adapter -> DVI in on Samsung HLN437wx DLP no longer works. HD stations and recording are fine. I have tried the unplug-replug of the stereo cables and several reboots of the box with no luck. Tried unplugging the HDMI to DVI cable and using component connection with L/R audio to TV and AV receiver with no luck. Any help appreciated.
Back to the HDMI issue. This started with the 7-22 software update though I had occasional issues in the past. Weird part is that after the 7-22 update, my HDMI to DVI connection would not work, but on reboot it was fixed and stayed fixed for over a month. Then, all of a sudden, I can't get a picture on my DLP via HDMI out on the box. If I unplug-replug, change order of power on, or reboot the HR-20, I can sometimes get it to work, but less and less frequently. Very frustrating as I don't get the same PQ on component. Feels like my investment in a HD set is wasted without being able to use HDMI connection. Oh, have I mentioned i HATE HDMI. This piss-poor standard has caused more consumer angst industry wide.