I was also considering the Denon 3808 but couldn't convince myself that I needed the extra features (networking, 4 HDMI inputs, 2 HDMI outputs, slightly more power) so much that it would warrant an extra £500 spend!
I bought the Denon 2808 in black for £600 and am very pleased with it. Nice understated looks, great sound, goes loud enough without distortion (my room is not big though), IMO great features (I can live with only 2 HDMI inputs) and it also doesn't run anywhere near as hot as the ONKYOs do.
The auto room set up seems very good and it is an all round good purchase, particularly at £599.
I would certainly recommend that you buy the 2808!