I'm currently using the M&M stack with T50RPs (BMF DBV 3) and I must say that I have been blown away by the sound quality.
There is a very noticeable improvement in all areas upgrading from my previous setup which was a Audio Kontrol 1 DAC/amp combo (not the greatest rig, I'm aware, but I've also heard other more high-end systems so I have an idea of what 'good' sounds like).
I definitely agree with everyone who has said that the Schiit stack is extremely transparent. While I could always tell audio sources apart before, the difference with the modi/magni is simply night and day.
But honestly, I can't stress enough just how good the magni AND modi are for the price. (btw I really don't understand the people ripping on the modi, IME it has performed incredibly well for the money and pairs perfectly with the magni). The detail, bass, mids, highs, sound stage, imaging etc etc are all fantastic IMHO. When I first started listening to the stack I was actually taken aback by how good the imaging was; you can pin point every detail/instrument in a song precisely. Oh, and the sound stage with the fostex cans is just enormous.
Finally, and this will most certainly upset some people, I want to note how this setup compares to the LCD-2.2s (in my humble opinion)... I recently had the pleasure of auditioning a pair of my friend's LCD-2s that he had paired with a Duet amp/dac. I listened to a wide range of music for about two hours on the setup and, as you can probably guess, it sounded fantastic. However, here's where I stand on this issue: the total cost for the audezes + the bare minimum amp/dac = ~$1200. The fostex + M&M = ~$350 after mods. From my experience, the sound from my modded fostex headphones is at least 90% as good as the LCD-2s AND the fostex are actually more comfortable (with new pads, suspension mod, etc), not to mention that I dont have to be nervous handling the fostex as they only cost a hundred bucks. **ducks for cover**
Anyways, I'm sure that a lot of people will be very upset with my comparison b/w the fostex and the audeze but for me, I just can't justify paying an additional $1000 for the LCD-2s.
I suppose I got a bit off topic... to summarize: the M&M is phenomenal and pairs very well with the T50RPs. For me, I believe that this setup is my end-game. At least until I make the plunge into tubes... :-)