For £99 it's worth just giving it a go. (At least you get a superb BluRay/DVD player and BBC iPlayer if CD replay is not up to expectation.)
I could give it a go for you, but that would involve unpacking and reconnecting my Naim CD5i and swapping my S370 audio output from digital (via DAC) to analogue (RCA) then repackaging the Naim again afterwards.
It still wouldn't be the comparison you are after. (You want someone to compare your Marantz DV6400 for you, not my Naim.) Plus I have no idea whether your tastes in music are reflected in my CD collection.
Anyway for £99 (less than Joel spends on a metre of cable) if it isn't quite what you want (in CD replay quality), you could put it in the kitchen or bedroom system or tuck it the back of a cupboard as a 'backup' just in case your Marantz ever needs repair. (It is a small unit and comes in a small box.)