I have had 2 Denon 2105 amps now and they have both blown up. But no worrys about why they blew up.. I think it was crappy speaker cable, but I am running QED now so it should be good.
How about trying the Yamaha rxv 757. If reviews are important, What Denon?? rated the 757 over the denon 2106
Also worth lookin into the Yammy 1500/1600 from Germany for arround £400. I would recommened looking into the Marantz range (if music is a priority) but the new amps 4500/5500 are arround and over your budget. Maybe a shop has a Marantz 7400 hanging arround then that would be a bargain for £400