I guess it comes down to how analytical you want to get, I'm sure that the Marantz will do an OK job and it will probbaly sound really nice, but I can't help feeling that adding at least a Rega Fono MM will add greatly to the presentation of the deck, the RP6 really is a great performer and I just don't think you will be maximising that with a built in phono stage of the Marantz, out of curiousity what cartridge will you be using, are you going with the Rega Exact?