The McIntosh AV processor is one way to go. Given that your Marantz AV processor is a good digital unit, another option is to upgrade with a McIntosh stereo preamp like C49 or C53. These 2 units have home-theater bypass where you have an option for full control from Marantz for watching movies. But for the stereo music listening with analogue (or high-resolution digital) sources, the stereo preamp will be much better. In the past, when I had an integrated system for both music and movies, I specifically required this "HT bypass" feature on my preamp and it worked out great.
It's great the your cartridge comes mounted by VPI. I still think you'll need the protractor for cartridge alignment in the future should you replace the cartridge. No rush for now, but something to keep in mind.