Need advice for a beginner.

I did that when we lived in the previous house, which was much smaller and I had the home theater and stereo in the same room.   I used a preamp with the high end power amps for the stereo and a home theater receiver for the home theater system.  That made it easy since I essentially had two systems in the same room.  

In your case, I suggest you use the 7012 for the home theater system, put the Martin Logans and McIntosh as your stereo system. Getting a preamp makes it easy to set this up.  Use tape out connections from the home theater receiver and feed them into the preamp.  You didn't say anything about analog playback, so a simple line level preamp will do the trick.  

I am sure some folks have alternate opinions, but I found for movies I don't need high end loudspeakers.  What I found I did need was speakers that play loud and have lots of dynamic range.   Think brute force being more important than finesse for sound tracks. 

That Marantz probably has a "Pure two channel" sound selector but all of the Marantz home theater receivers I have had in the past produce inferior sound quality using this feature.    Granted I have not owned the one you have, so maybe on yours it will work fine.  If so, that is an alternate option.