Hi Smanley - I'll expand on my thoughts since it was I who voiced the heresy in the first place.
In my experience, the benefits of a 600 CD player over, say, a 300 player are subtle (ie not night and day, when comparing the best at their price levels) even when played through an amp (or speakers) designed first and foremost to produce high fidelity stereo.
Whilst AV receivers can undoubtedly make quite a good fist of stereo (my Yamaha among them), they come with inevitable compromises - you're paying for an awful lot of electronics which mean that they have to be jacks of all trades and will not wring the best out of high quality stereo source components. I therefore argue that if you're going to put a CD player through it, your AV amp is going to stunt it anyway, so you might hear no difference between it and a 250 quid Cambridge. Best example of this is that the noise floor (hiss, hum etc) is higher on my AV amp (I presume because of all that trickery) than on my stereo one.
I think it would be worth your while taking your Denon with you to hear the Apollo through it, and comparing it both with a cheaper CD player (sadly you won't be able to audition a Cambridge in a Rega shop - borrow one if you can!) and to the sound you'd get with a comparable stereo amplifier - for example, Rega's previous Planet and Mira combo were the most *fun* (whilst not strictly neutral) I'd heard in a long time, but the player became a pale shadow of itself when played through my Yamaha - harsher treble, soundstaging disappeared, blah blah.
But above all, trust your ears - if the Rega sounds better (350 quid better is your call), it is, and you can safely ignore me.