Magnifiscent is SO right -- the two are nothing alike. BK is (again) even in a different fragrance family than Kouros. Why YSL chose the confusing moniker I'll never know.
Body Kouros is like M7 for me in that I TRIED to love it -- I really did, beeswax note and all. I finally ended up swapping it (along with some other things) this past week for some Santa Maria Novella Musk. I'm glad I swapped, as a) I shouldn't ever have to work that hard to make myself love a frag and b) I made the other swapper happy.
I'm surprised that BK is still on the market and not dead as disco, honestly. Why? Because it IS very different, even cutting edge stuff. Very well blended stuff, this, and the quality of ingredients cannot be faulted -- don't get me wrong . . . but mainstream it ain't. I genuinely like Body Kouros, yes, but I cannot say that I love it, nor that I want to keep a bottle around (obviously). I just can't bring myself to fall in love with it and make it a "regular." (And when you have damn near 60 fuckin' bottles on your bureau to begin with, this DOES become an issue.)
Kouros, on the other hand, I ADORE (even though many others despise it). It is, IMHO, a sexy, animalic beast, masculine and feral and nasty. (It's a Big Eighties frag, true, but that's just about my favorite genre of frag to begin with, anyway!)
Do yourself a favor and sample Kouros before buying or swapping for it. It's kinda like Vegemite (or Rob Zombie flicks, for that matter) in that it's definitely an acquired taste. (Just 'cause I love both doesn't mean that everyone else will concur.)