So, after listening most of the day, I'd say we have a winner with the M1060C.
I have two comparison cans. For the M1060 showdown, I have M1060 opens with Audeze vegans (no other mods). And for the closed showdown, I have MrSpeakers Aeon Flow Closed.
Here's the AFC comparison first (M1060 open comparison to come later). In terms of tonal balance, I find the 1060Cs to be a reasonably close match for AFCs. They are both a little on the warm side (which suits me perfectly). However, there is substantially more bass in M1060Cs than in the AFCs, especially in the sub bass, but it seems to be nicely focused. Mids are well present in both. Isolation is quite a bit better in the AFCs but not terrible in the M1060Cs. The key difference for me is soundstage: the M1060Cs win this hands down. Much better sense of depth and 3D immersion than the AFCs. Pretty amazing for a closed can; almost as wide as the M1060 opens. So it's close call, but I would reach for the M1060Cs before AFCs.
BTW, I think it's important when reading the opinions here to know something about the listening preferences of the person providing the info. The end-game headphone for me is the LCD3. I find HD800s and Beyer DT1990 pros to be too bright and fatiguing. I value a certain warmth and sweetness and, most importantly, I value soundstage and a coherent sense of immersion. Don't really care too much about whether a set of cans is perfectly neutral etc. as long as it has these features.
. But not complaining too much. They are a great value at full price.
But I did save myself $352 
