To get the 'best' out of the Marantz unit, you would need to look at something like the PMC DB1i at many times the price you are talking of spending.
However, something like the MA BX2 would work superbly well and give you a good level of performance. If you can stretch to the RX1 or some Rega RS1s you will get even more out of it but you need to audition these combinations to see what works best for you.
I know Chebby on here has one (I think). He uses Rega RS3s I think. Though I imagine he will have looked at a few on his travels. Perhaps a new thread directed at him? Do doubt he'll find it on his own of course . .
If it hadn't been for my Rega R3s coming available (at a very good price in mint condition from a friend here) then I would have bought either Monitor Audio RX1s, RX2s or Castle Knight 2s.
That's not to say any of those are 'best'.
I try not to personally recommend equipment any more. (Especially the M-CR603 and/or speakers to go with it.)
WHF? tested the M-CR603 very successfully with Boston Acoustics A26s so they are an option to try out. Gramophone magazine successfully tested the M-CR603 with PMC DB1s (and GB1s) so DB1is should be worth trying if your budget will stretch.