Hi Ronnie,
Have to put on my thinking cap and hop in the way-back machine...and of course there's the whole "US market differences" thing to consider; but here we go.... In the US-spec Avant's you press Menu twice to get to the set-up menu enter the 'Sound' menu, then 'Speaker Mode' within which you can change the default for Video from 3 to 5. Naturally the Euro version is likely different in detail, but I can't imagine that it is so terribly different.
Then again, I've just taken a quick spin through the UK user's guide and there is a warning that the TV may auto-select 3 or 5 based information contained in the audio signal. See page 64. So, perhaps I have rambled on a bit too long and unhelpfully. Oh, well. Call me an Anorak.
We kid because we love.
Bang & Olufsen Tysons Galleria
McLean, VA USA