Are you needing speakers also? Because the AVR is going to be £650 alone, than any decent speaker will be at least £150 if not more. For Atoms you need 7 main speakers, 1 subwoffer and at least 2 ceiling speakers. That makes it 7.1.2. The cost goes up even more from there.
My front speakers alone was £775 so you looking at £3174 before it even becomes worth it. If you buy everything used you might get away with £1500.
The Denon is okay and better than most brands at that price range. I cannot comment on the speaker package. A long time ago I bought a 5.1 speaker package and thought it was amazing. Than I heard some real speakers a few years later and realized I was scammed. Did some reading and found out to either go with a set a entry level speakers or get a sound bar. None of those package ones. They are beyond cheap and sound no better than a good tv speaker. Polk and Klipsch isn't bad for what you get out of them.
I started with Polk Monitor 50s , than switched to Klipsch reference series and next year I'm going to just build my own set.
I personally wouldn't spend less than £1000 on speakers (for 9 = £111 a speaker). Below that its just a waste of money.
I'm not looking to spend any more than my stated budget, so spending £111 per speaker is out of the question, regardless of how much better it might sound, I'm no audiophile and don't care enough to warrant spending more.
I'm just looking for something I can get that meets the spec for the budget and is an upgrade on my current setup.