It appears the Crucial site is messed up!
If you use their wizard to find RAM, it only shows 2x8GB for the XPS 8500. When you click "Show all compatible..." below that entry, the next screen only shows 2x2GB. Now look near upper right corner of the screen and you see that 2-piece kit is checked. If you now check single, it suddenly shows a whole bunch of other options including 2x4GB for $41.99. DUH!
Compare specs with what Osprey found at Newegg and if they match, add in tax and shipping to see which is the better deal. Image may be NSFW.
Clik here to view.