I'd get the x-ls and x-sub now, use my current bookshelves (JBL LX22's) for my new rear channels and and add in an x-cs and two more x-ls's to replace the rears later...
Right now, that would run me $420 before shipping (no tax). I know they're heavy, so shipping could be about $70-$80.
OR
Infinity TSS-1100 5.1 package for about $500 (including tax and shipping). This is a refurbished model that included the original factory warranty.
Let me know what you think! Thanks!