You'll love the MacIX. I used mine many a time; Spamburgler used on the Roan Higher Colder Hang this past January at 8F and 40k wind. It's just that when it gets warmer and the snow/ice turns to liquid, well that is what motivated me into a waterproof/breathable sock that could be used year around. The material we chose (bet you saw this in several vids) was the w/b cuben...the cost of it is crazy and there was never a big demand for anyone to do a huge production run. The sil/dry duck alternative was just as functional only heavier. The only one I know who was doing anything with either was Hangnout and last I talked to him he was covered in work.
Personally I've now over 60 nights in a w/b sock and have now gone the entire 12 seasons using one or two or three (the Dirigible, the Graf, and the AirShip). It was a fun project, mostly because we were blessed with being able to work with and test for Hangnout. I'd like to tell you I'd hoped many hangers would have gotten the w/b 'bug' but each of us has a different slant on what it is to hang in those piney woods
and what we want to carry. The AirShip was the (duh) 3rd incarnation, and thusly was the most advanced in terms of weight:feature ratio....at 12 ounces it does more than the Dirigible weighing in at 4 ounces more...but if there were only one I'd still gladly carry the Dirigible at 16 ounces simply because for it's weight it still had more purpose/function than many a sil tarp of only 4 years ago.
This doesn't help you seeking the w/b sock I know but you never know what a PM to the right person may bring.