get some component cables for ur xbox, then go to display settings in xbmc and set to 1080.
the only reason I left XBMC is because my xbox fried itself, the PS3 is good at streaming but you need a fast pc with and Tversity setup correctly for it to be successfull.
I'd stick with XBMC if its only for streaming atm, unless you really want a PS3
, hopefully sony will increase their codec libary soon.