Well, I've had Maverick for two weeks and I have to say I love it. Use it primarily as a DAC, though it works well as a headphone amp as well. The sound is beautifully detailed and very pleasant to listen to even after long hours. I'm running it through the tube (6n3) that came with it, I have already purchased a couple of other tubes to play around and see what works best. Anyway, after a week of burning in Mav sounds great and it's an awesome buy, it looks pretty attractive too.
As for the opamp speculations, quite frankly I don't give a damn what they put in it, the fact is it sounds great and if it takes horseshi.. to make it sound good I'll take it . By the way, Benchmark dac1 uses NE5532 and costs $1000, read this post
NE5532 Opamp - Benchmark so it shouldn't be that bad ... there soooo many variables to make a good DAC ... Having said that I have no clue what opamp is inside the Mav, but it's doing the job well. I think that all three versions are pretty much identical, you just have to make a choice you're most comfortable with, sound-wise /price-wise you can't go wrong.