Pioneer SC-LX801

I have some thoughts but I would need to get a look at those schematics. Send some links.

Sorry about the download link(did not download it myself). This is the first, that I have seen Elektrotanya posting a user manual.

I also have an Epson 2045 to repair as well. Sometimes there is no HDMI signal, but the menu works.

Based on your symptoms and what you have tested so far I would think that the problem may be in either the ADC section, DSP or DAC section. In the manual, I saw some areas to check some line voltages so I would probably start there. A quick look on pages 46, 70 (audio and ADC, DAC) for some voltage checks. I would not be thinking a lot into DSP just yet since you have all firmware's. Although slim, I would not rule out the volume/switching ic's yet either. Although they appear too be working in one aspect another part of it may not be. Good luck hunting.