I've used all the codecs.. bit more of an update.. the frequency is significantly less often than 30-60 minutes now I've changed the TV settings.. more like a few hours - I can live with that as it doesn't go off several times in one program!..
it does point to HDMI.. I tried swapping my XBox and HTPC cables over but it didn't help - they are both are both cheap ones although the XBox never drops out using either cable. I could try a better cable