Change settings level per internal team discussion + audio passthrough defaults changed

See the spreadsheet mentioned here: http://forum.xbmc.org/showthread.php?tid=163982

I avoided any of the "unsure" comments.

Changed audio passthrough defaults per other discussion about how audio should just work for most users out-of-the-box, but probably a moot point once the new audio stuff goes in: http://forum.xbmc.org/showthread.php?tid=170544