Interesting, I got the exact same problem! You can check my post here: https://forum.beoworld.org/forums/topic/beolab-8000-turn-off-after-some-hours/
Thats a coincidence, seems like the same problem indeed. Did you find anything yet? I removed the amp, but I cant see anything on first sight. I think I need to assemble it again and do some measuring when its powered and in standby.
Ill also try if I have the same problem using a Powerlink adapter to RCA.