than sound quality its likely there is only a marginal difference in sound quality between the M-CR603 and a PM5004. Biamping using the passive crossovers in the speakers will not be worth it as a lot of power is wasted striping off unused frequencies in each section. If you want to use a turntable with that unit you will have to use a phono preamp. If you are strapped for cash get the Audio Technica AT-PEQ3 in closeout for $44.

From the Marantz literature, "or select biamp mode for double the power into a single pair of loudspeakers." This is a false statement as most of the power is converted to heat as unused frequencies are striped off in each section. It would be true if one could use active crossovers between the preamp and power amp which is not the case with the M-CR603. Just use the "Speaker A" configuration in the connection and "SPEAKER SETUP" and leave the binding posts bridge in place on the B&W 685s.