For me, one of the best CD players under £500/600 would be the Rega Apollo, which will also leave you with a fair bit of change. It's especially suitable for those that aren't too keen on CD's brighter/harsher treble.
I have read a few reports about the Sony SCD-XA5400ES ....
not sure if that model has been replaced, but some people who own them were stating that it was better than cdp's that cost considerably much more (in the thousands)
perhaps an ex-demo model can be found within your budget and perhaps worthwhile auditioning?
£750 (seller is open to offers) gets you this Moon CD1 ... 5 star rating by WHF
these are just 3 examples of what can be found on the 2nd hand market, and I am sure if you research and are patient, you will find a real bargain somewhere ....
don't be afraid to buy a good used cdp (mine is old, and I use it almost daily for more than a year, and never misses a beat)
Got my Cyrus CD8x for £350 and it's very, very good. Agree with Arcam recommendations too, i had the CD73t previously and have read great reports on the 192. Had the NAD C521BEE also, that was good so the other NAD's i'm sure should be a safe bet.