I was making this same choice in November, last year.
I auditioned the MA's locally, and read all the reviews on the 6T's and RX6's speakers/systems that I could find.
I concluded that they had a similar type of sound from what I had read (both well reviewed), so I ordered a full Aperion system for the 30 day trial (including their new Bravus 12D sub). I figured if I didn't like the sub, or any of the system I'd send it back. I was really planning on a SVS sub with either the MA's or Aperion's.
Well I loved the 6T/6C/5DB part of the system right away. It took me a little while to get the sub totally sorted out, but it was tight and musical right from the start.
I ended up keeping all of the Aperions. I am more than pleased with them. They have rekindled my love of home audio and I still look forward to listening time.
The MA sub is ~ $1500 here locally. I paid much less for the Bravus.
So you really can't go wrong with either system, but I would seriously consider a sub from those mentioned above, especially if you go with MA (not that their sub is inferior, but it is pricey, and I'm sure you can do better, and for cheaper).