They are basically the same unit. The 8001 does everything the 7001 plus:

Different power supply with Troidal transformer and more WPC. 110 vrs 125
It has two HDMI outputs vrs one.
It has added multi room function (don’t remember what).

And from what I can gather by participating in the “official” Marantz thread at AVS, my 8001 would appear to be the only Marantz that processes 6.1 / 7.1 discrete PMC audio streams, or post processes 5.1 PCM audio streams. I suspect that some of the users who are reporting that theirs don’t do this may have problems with buttons on their remotes. I have never been so lucky to be the ‘only one’ in a crowd where good things happen.

You can download the manual and look at the notes. They share the same manual and wherever there is a difference, the notes tell you “8001 has ***”.

I do miss some the functionality that the HK had, and presumably the demons have, but not so much that I’m loosing sleep. It sounds so friggin good, I can put up with some loss of functionality.

I does not up convert, so if that’s important to you, you’d be better off with something else.