I have been digging into properly setting the aspect ratio for my LED HDTV from samsung as well. The only problem I am facing is the firefox browser menu fonts are huge. and so does the KDE desktop fonts are huge.
What I found a temperory solution is go to KDE desktop and under appearance settings ----> fonts you need to set the dpi settings for the fonts.
Now coming back to the resolution , I found an article on some other forum,
I know some people here do not like xbmc, I am not favoring them but we can use their/ubuntu's guide.http://forum.xbmc.org/showthread.php?t=54685
in these steps the difference would be some command should be according to our system, for example killing the xbmc live ,, i think ours will be kill the startx and then move on,,
Perhaps , a dev can come out with exact steps and this could be a great how to... for our wiki.