Hi Demet,
Welcome! I have the 60.500 system and I know it will prove to be AMAZING for you. Prepare to re-listen to every CD in your collection and replay every DVD you own because it will be like watching them for the first time again.
There is always that piece of gear you wish you waited for and the 3808 is the one I wished I waited for. But I am very happy with my 3806. It does everything I need and plays the Axioms effortlessly so I must assume the 3808 will do just as well.
Depending where you live, compare even the speaker wire pricing to online sources. In my spot here in Atlantic Canada, very nice 12 gage speaker wire (covered for in-wall use) from Monoprice was WAY cheaper than the 12 gage bulk wire at my local Home Depot (not in-wall and frustratingly hard to bend) . Delivery was swift too for a cross border purchase.
Sounds like you have already done lots of research but just in case, the Axiom Articles section off the main page has some excellent guides on designing and setting up a home theater. The article on speaker placement for 5.1 and 7.1 has some excellent diagrams that I refer my friends to a lot because they are so visually simple to understand.
Have fun, enjoy and tell us about your first impressions once they arrive.
