Though I'd share my experiences with my new SR6005. I've had it for about two weeks and I like it a lot.
I went with this unit for the HD audio decoding, Audyssey MultEQ, and pre-amp outs. As of this past Friday I also have the unit hooked up to a NAD T955 five channel amp. The amplification side of the Marantz is very good but doesn't stack up to a stand alone amp like the NAD. In my opinion AV receivers are becoming like digital cameras with new digital features and improvements that quickly make older models pale in comparison. Figure on replacing yours every few years or so if you want to keep pace. I tried and sent back a NAD T775HD that I got on sale in part because of their modular design. Unfortunately, it had a number of bugs and quirks that I didn't like and decided to go with separates instead. I flirted with the new SR6006 but decided the 6005 had everything I wanted at a good price. I don't really like the whole port-hole look of the new ones either.
I like the OSD and the over all flexibility of setting up inputs on the 6005. Although it took some time, I was able to set up all my inputs and rename things. I couldn't imagine setting everything up without the OSD. I found the Outlaw Guide for the 7005 covers everything the 6005 does and has some helpful tips. I find the Marantz manual to be OK and similar in design and layout to an older Denon I owned. There some features like the adjustable mute level that are also the same as Denon. Its pretty evident that Marantz and Denon are part of the same company. I think that's actually good cause it gives them access to a larger R&D department that has sorted out all all the different digital audio, video processing and HDMI issues. Something I can't say for NAD
The Audyssey set up went off with out a hitch and pegged the speaker distances on the first try. As expected it made a significant improvement in imaging and sound stage and I generally keep it on. The NAD T775HD I tried had MultiEq XT and honestly I've come to believe that straight MultEq gives most of the same benefit as XT. On the NAD at least XT was a lot more finicky and sensitive to ambient noise and gave reverse phase warnings that weren't true. The Marantz gives great adjust-ability on how much DynamicEq and DynamicVolume you want and remembers your settings according to each source. That's cool cause I use quite a bit of Dynamic Volume to squash the volume bump on commercials while watching TV but don't want so much when watching Netflix.
Dolby Headphones came as an unexpected surprise and I've already tried it once while watching a loud movie late at night. The surround effect isn't quite as convincing as an actual 5.1 setup but it was good enough and I'm sure my neighbors appreciated it. I find my self using Dolby ProLogic to convert stereo Netflix sound into surround and it does a remarkably good job. There's a confusing number of choices for different audio processing depending on the source. The Outlaw guide gives a nice explanation of each and recommendations for use to start out with. Even so I still have a way to go getting to know each and the various options possible.
In the end, I'm happy I sent back the NAD T775HD and went with Marantz paired with a NAD amp. Feature wise I think its richer and better implemented. It works faultlessly as a pre/pro and even though I went with an external amp, for the time I was using the internal amplification I found the sound quality to be very good. Obviously many people are happy with the way their sounds as is.