I just purchased a pm6004 and cd6004 to use in a secondary system. Only listened to the amp a few times yet (waiting for a new media stand so I can set things up), but I thought it sounded great, even without break-in time. Can't say how it compares to the Rega, but I've heard the Rega's highs are a bit harsh. I can tell you the Marantz is on the warmish side, and pretty dynamic.
By the way, if you go for the Marantz, I recommend Music Direct (musicdirect.com). They gave me $100 off the amp and cd player because I bought them as a set, and they shipped overnight for free (!). They also threw in two aftermarket audiophile quality power cords for free. Best service I've ever had over the net.