I'm getting the stock AK 100, complete with 22-ohm output impedance. Yes, it worries me, as my UERMs have a rated impedance of 21 ohm @ 1kHz, and are probably less than that below 1kHz if their impedance-to-frequency behavior is similar to other UE customs that have been measured for that. I thought about getting the RWA AK-mod. But ...
(1) Chris at CA, who is not an idiot or a buffoon, reviewed the stock AK using UE 11 Pros, and didn't report hearing any of the stuff that we would normally ascribe to an impedance mismatch. Shigzeo asked him about it directly and specifically in the comments, and he stuck to his guns.
(2) If the apparent impedance mismatch isn't a problem, I saved $200 by buying the stock model vs. the RWA mod. If it is a problem, it goes off to Vinny and I'm out $250 for the mods. Seems like a bet worth making.
Damn, it takes a long time to load a 64 gig micro-SD card.