Based purely on what others have said (reviews, word of mouth, instore kit I've heard), I think the NAD gear gives you a very dynamic sound, good detail, without being overly bright; possibly the kind of thing you could easily sit down with for an evening - not stressful on the ears, in other words.
In terms of how it would mix with other kit, I think NAD partners well with a wide range of other manufacturers gear, though I might steer away from very warm sounding equipment else you risk ending up with hi-fi in the comfy slippers mode! Some people like that kind of sound though, so don't write it off either.
Marantz would be more forward I think, just as detailed but with a more "open" sound; I like good detail in the playback and I want to tell the difference between the instruments with a good sense of space between players. My current set up gives me a good feeling of realism and involvement in the music with traditionally trickier instruments to replicate coming over particularly well - grand piano, bass kick drums/floor toms - however, whether it's the "best in show" is another thing entirely.
I'm definitely not saying the NAD wouldn't do this, but given the choice between - and especially - the KI rated Marantz gear and a standard 320BEE, I'd be leaning towards the former over the latter. Even the standard OSE Marantz variants are good, but maybe a slightly closer call.