The only thing I would say about the Denon is that they tend to fudge the power specs a bit. The Denon PMA710 is really 55 watt per channel to 8 ohms. Nothing wrong with that, that's plenty of power. But it takes some digging to actually find it.
At £600, I would divide the budget like this, to establish a starting point -
£200 = CD
£200 = Amp
£200 = Speakers
Though there is a great deal of flexibility on that.
At the top of the list, would be the Yamaha AS300 Amp (60w/ch) and the matching Yamaha CDS300 -
£207 = Yamaha AS300 amp (rated best amp under £500)
£199 = Yamaha CDS300 CD
£220/pr = Wharfedale Diamond 10.2
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£626 = TOTAL
£225/pr = Monitor Audio BX2 (Alternate)
The Diamond 10.1 were the "What HiFi?" Product of the Year in 2009, and the Monitor Audio BX2 were Product of the Year in 2010.
If you want to scale back a bit on the speakers, then the Diamond 10.1 are £170/pr and the Monitor Audio BX1 is £180/pr.
A new speaker on the market and worth considering, the Dali Zensor 1 for about £180/pr.
If you can go a little higher on the amp, then the Yamaha AS500 is currently £250 for SuperFi.co.uk.
The Marantz PM6003 (45w/ch) is about £220 from RicherSounds.com and SuperFi.co.uk. The matching Marantz CD6003 are in the range of £200 to £250. Both models have been replaced by 6004 models. (CD6003 = £199 at RicherSounds.com)
You may like the Onkyo RX-8255 AM/FM Receiver (55w/ch) for about £220. The Onkyo C7030 CD Player is £179.
AVBristol has an excellent deal on the Denon PMA510 (45w/ch) + DCD510 for a modest £370 -
AV Bristol - Denon PMA-510AE & DCD-510AE
PeterTyson.co.uk has the Denon PMA510 for £149 and £159 for the matching CD Player. PeterTyson also have the Marantz 6003 series, but you have to call to get a price on the CD, either the price or stock levels are very low. The Yamaha AS300 is £199 from PeterTyson and £179 for the Yamaha CDS300.
Staying near £600 should be easy, trying to stay at or just under £600 is going to be more difficult.
Staying as close to £600 as possible, I think these might be your best choices.
And to some extent, it depends on how determined you are to buy everything from the same source -
£249 = Yamaha AS500 (80w/ch) @ SuperFi
£179 = Yamaha CDS300 @ PeterTyson
£169/pr = Wharfedale Diamond 10.1 @ SuperFi and others.
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£597 = TOTAL
Though I would rather see this system with the Diamond 10.2 or Monitor Audio BX2. That would mean a new total of £648 to £653.
Or
£199 = Yamaha AS300 (60w/ch) @ AudioAffair.co.uk or PeterTyson
£179 = Yamaha CDS300 @ PeterTyson
£220 = Diamond 10.2 many sources at this price
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£598 = TOTAL or £5 for the Monitor Audio BX2
I think those are about the best systems you can come up with in your price range.
But then ... that's just my opinion.
Steve/bluewizard