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. 

@spatialking Pure Direct, I believe that’s what you’re referencing.  Unfortunately, your Marantz doesn’t have home theater pass-thru; which that would allow you to purchase a dedicated 2-channel preamp, have it in line with your Marantz, and allow you to utilize the rest of your components.  

In lieu of that, I would investigate purchasing a DAC, that can operate as a preamp, too.  PSAudio and Mytek come to mine.  I will share that I’ve used PSAudio’s Direct Stream Junior, in conjunction with their NuWave Phono Preamp over the I2S protocol and it sounded unbelievably good.  I A/B’ed against my Moon phono preamp, and, well, I got rid of the Moon.  Nonetheless, purchasing a DAC and using that as your source input, fed thru your Marantz will allow you to use your amps and subs.  When you move to vinyl, you can just unplug your interconnects from the Marantz and plug them directly into your DAC, you won’t use your subs while listening to vinyl, so those become a moot point.  Some likely do, but there’s some logic associated with why some don’t.  Isolation of the turntable comes to mind, lack of a low pass filter on older mixes, a lot of mucking about with sub levels to get it right and such.  It can be done, and others will likely chime in, stating why I’m wrong.  Ultimately, you’ve got a great home theater pre, has all the bells and whistles, so getting rid of it and getting something with HT pass-thru probably isn’t worth it.  Hence, I believe getting a DAC that can operate as a preamp will solve your 2-channel pursuits.  Additionally, if you’re moving to vinyl, I would strongly recommend getting an external phono stage and bypass the internal Marantz one.

The short answer is yes, you can absolutely incorporate a very good 2-channel system within your current system, and it's super easy.  My strong recommendation would be, if you like the sound of your Macs, buy a stereo preamp that mates well with them sonically, and with one extra pair of interconnects, you're good to go.  The Marantz is a huge bottleneck to your 2-channel performance, so you need to get it out of there for good stereo sound.  Here's how...

You just run an interconnect from the front L/R preouts from the Marantz to the HT pass through on the stereo preamp (or any unused line-level input if there's no HT bypass), then run an interconnect from the outputs of the stereo pre to the inputs on the Macs.  Then move your stereo source output also from the Marantz input to an input on the stereo pre.  That's it -- you're done!

The only thing is that if your stereo pre doesn't have a HT bypass feature, which is fine, you'll need to set a reference level on the stereo pre for when you're doing HT so the front L/R speakers have the proper volume level relative to your other HT speakers.  I just used the 12:00 position on the stereo preamp's volume control because it's easily repeatable, and then reset the channel balance again through your Marantz as usual. 

With this setup, when you listen to 2-channel the Marantz is COMPLETELY out of the system and has no impact on sound.  I think this is what you were looking for.  Hope this helps, and best of luck!

Add the McIntosh tube preamp that has Dac built in, and connect the bluesound to it, and set up the HT passthrough on the McIntosh. Unless you had a high-end HT processor like a Theta Casablanca III HD/IV with Extreme 2 Dacs which has an outstanding preamp for 2 channel the Marantz is going to be your bottleneck. There is no substitute for an amazing preamp. Also, run Balanced XLR to your 501’s. 
My audiophile friend is running that McIntosh tube/dac preamp with 275 Mac tube amp and bluesound 2i into the Dac section and it really improved his system and he has owned Mcintosh solid state amps before

Thanx for all the advice,  can you tell me which Mac tube preamp would do everything you suggested.  Thanx, jp

Mcintosh C2600 preamp has an integrated DAC that my friend is using. upgrading the tubes via Kevin at Upscale audio added even more clarity