Onkyo 605 - surround sound modes

[Juzzie Wuzzie]

Sky HD feeds into my Onkyo 605 via HDMI and optical for sound. I have a 5.1 system. What surround sound setting should I use for it to pump the sound through the centre speaker if it is an ordinary broadcast yet gives the best surround sound experience for programmes in Dolby Digital - i.e. Lost? Same for DVD? In short, I just want the Onkyo to select the best mode,

 

[Andrew Everard]

Choose Dolby Pro-Logic IIx Music for day to day viewing. The receiver will automatically switch to Dolby Digital if there's a suitable soundtrack on offer.