I can't really comment on the V6. I elected to not listen to it, as I was really wanting something that wouldn't fatigue my ears (I have issues with fatigue from treble, but I really enjoy treble, so it's been a struggle for me.) and I wanted something that sounded balanced. Now, I can't comment on the V6, but I certainly can comment on the A6 and compare it to what I've heard about the V6 and I can compare to the SE535, so hopefully you've listened to one at some point so you can have some point of reference.
Now, first off, it really should be pretty similar. The A6 is a very, very balanced and neutral sound signature. When I listened to the SE535, I found that it would fatigue my ears within about ten minutes due to the treble energy (and they don't have especially bright treble). The A6, I would say, had treble with more energy than the SE535, but (and I assume that the Adel module is the culprit here) the A6 had no noticeable fatigue for me, and sounded absolutely excellent. To my ears, it sounds as natural, more so even, than the HD650, and it was incredible. Very detailed, and well balanced. Balance between all frequencies was above something like the HE-500, and the detail was amazing. The Adel module makes a VERY noticeable difference to my listening, and I was incredibly impressed by it. In my listening, the Adel module does everything 1964 says it does. I haven't had a chance to listen to the A6 for hours on end, as I don't yet have mine in hand, but I doubt I would have any issues leaving them in my ears, playing music for 12 hours or longer (and I plan to do just that on an international flight I have planned for this Thanksgiving). Let me put it this way: They sound better to me than anything else I've ever listened to, with the only exception I can think of being the $40,000 full size 2.1 floorstanding speaker setup that my family used to own. The only things I can think of that tie the A6 for me are some very nice speaker setups at my local speaker shop. (disclaimer: They didn't have the A8 on hand at the meet, and I didn't listen to the A10 because I didn't want to be influenced into buying something far outside of my already stretched budget, and I was already $100 out of budget for the A6...)
Oh, the bass... I forgot to mention that... It's very flat sounding, as far as quantity goes, but the quality is astounding, and it reaches down to the deepest depths. It went as low as my Denon D7k (which goes really, really low) but it was much better balanced than the aforementioned Denons. The bass never reached into the mids, and never affected the treble. And mids are wonderfully natural, and vocals are some of the best I've heard. Very, very impressive.
I certainly preferred it to the A12, which to me has too much bass, and has a slightly weird sound. I'm not sure why I find it so odd, but something doesn't seem quite right about it. (Note: That may very well be due to the fact that I've never listened to $2,000 headphones much before, so I don't really have anything to compare to in that price range.)
The A6 are very, very good, and to my ears, they punch above their weight for what I would expect for their price (even at their MSRP).