ebaierl wrote:...The living room TV, where I want to use it, is a 2009 Sony Bravia...
I have a Sony Bravia of similar vintage with 3 HDMI sockets, and a second, newer Sony. Both work with correct config.txt settings.
I have noticed in the past, that the newer Sony was not showing anything while booting, but OK once GUI desktop loads. I just assumed this was a resolution mismatch.
I can try to extract the config.txt later today if you think that will help.