Among my amps is a WA22. I do not own an Abyss AB-1266, so this response is strictly limited to the issue of the general ability of the WA22 to drive hard to drive headphones well.
I own an LCD3 and an HD800. I've owned the LCD2, both R1 and R2. I've also owned an HE6, I've sold all of these but the LCD3 and HD800. Therefore, I have some experience driving headphones that aren't among the easiest to drive, particularly the HE6.
When considering the WA22, one must appreciate that it's really two different amps, depending on the power tubes used. If the 6AS7/6080 tube family is used, then the WA22's power output is lower than it could otherwise be and the WA22 might be better used for easier to drive headphones. However, the use of the WE421a/5998/7236 tube family changes the WA22 into a very powerful amp capable of driving even the HE6 well (though how well is, like everything else, a matter of opinion). I was never as much a fan of the HE6 as some are others here and sold it after not very long. Therefore, my experience with it is much more limited than with some other headphones and I want to be careful expressing anything approaching authoritative opinions about driving the HE6.
I consider the WA22 perhaps one of the best bargains (for some people, that's a poisonous remark) available in fully balanced tube amps. It is wonderfully musical, if driven by the "right" tubes, and it has a huge choice of still reasonably priced and available tubes. If it has a weakness, it's its lack of pre-outputs but that's not a significant drawback for the large majority of people who would be interested in the WA22. It's fully balanced, in and out. It has both twin 3-pin and a single 4-pin output plus a single ended output. It also has switchable balanced and unbalanced inputs and a selectable high and low impedance power switch. Given its musicality, wide range of usable tubes, modest footprint (for a balanced tube amp), and cost of just under $2K, it's a great amp.
I recommend the 5998 over the 7236 simply because I find the 5998 more musical though it is less economical. However, as between the WE421a and the 7236, I think the 5998 hits the sweet spot of power, musicality, and economics. The ultimate is, of course, the WE421a, but these are much more costly than the 5998, which are much more costly than the 7236. All sound fine and few will be disappointed with, for example, the Sylvania 7236 (or, more especially the harder to find Tung Sol 7236), even though my preference is the 5998, as stated. Use your favorite drivers (generally, the 6SN7 class) and rectifiers (generally, the 274b and 5U4G classes) and you just can't go wrong with the WA22. With the higher power output tubes recommend here, the WA22 will be able to drive almost any headphone well, particularly the LCD2 or 3 and the HD800. Though I think the WA22 can drive the HE6 well, I don't want to stick my neck out quite so far for that claim and judgment is best left to personal audition at a meet or otherwise.
Good luck and keep this great amp high on your list unless you're among those for whom a $2K headphone amps would bring embarrassment to you or your family (to say nothing of the cost of its tube complement).