In strict definition terms, an AV amplifier would not include a tuner or any kind of processing e.g. Dolby / DTS decoding or any kind of scaling chip etc. In practice, the only difference tends to be a receiver has a tuner, an amplifier doesn't.
I thought that was the case, but Pioneer's website lists the VSX-LX50 as an AV amplifier, yet a 30 preset channel tuner is listed in the specifications.
Mate, haggle your backside off. You'll get the Onk for closer to £300. I'll bet you could get it for £350 with no trouble and £320 with a bit of work. Give it a go. Also don't forget the Denon 1909 did very well on test recently and beat the new Onk but it does retail at £450 so maybe not. Try and get the Onk at a good price and report back!