What speakers do you plan to drive with this amp?
I have not heard the MR (sorry) but I'm yet another AVA booster. Over the last 20 years I've had only two amps as long-term items in my system, but have tried many others for comparison (Muse, Moscode, Krell, Quicksilver, Adcom, CJ, B&K, White Audio, Plinius, some others I can't recall offhand). I felt the FetValve 550EXR, when I got it, was the new keeper. Musical, transparent, powerful. It really doesn't do anything wrong. The right choice (assuming a good equipment match) for someone who is looking for a great amp without any sort of "additional" character. Not the amp if you need to tune the sound of your system (which is sometimes necessary). The upgrade to the Ultra provided additional improvement in low end articulation and top end extension (without being grainy or harsh).
BTW, it's not to say some of those very expensive amps didn't sound good in my system. In some cases they did, and very nicely. But I didn't find anything that was "X" times better in support of their price being "X" times greater than the AVA.