Hi mate,
I have owned my Marantz AV8003 Surround Processor/Pre-Amplifier for a couple of months now. As you can see in my signature, it is mated to a NAD Masters Series M25 7-channel Power Amplifier.
Sonically, I am very impressed with the AV8003. For me, sound quality is top priority, so I am very happy with it. I used to own an Integra DTR7.8 A/V Receiver (which is pretty much an Onkyo TX-SR875 but with fewer 'bells and whistles') performing pre-amp duties, and the difference is significant.
The Marantz AV8003 is much more natural-sounding and much more musical.
Video processing side, which I don't really use, is apparently not that fantastic, but for what I need the AV8003 for, it is wonderful, and I am extremely happy with it.
The Onkyo/Integra kit tends to head towards the more 'exciting', 'ballsy' sound, which seems to impress on short auditions, but I have found that the Marantz has found a sweet-spot with me.
Rotel makes fabulous gear, and the Rotel RSP1570 is extremely well-priced (at least here in Australia, anyway) and should be good, but I have not listened to one, so I cannot make a comment on it.
Dan.