for 00-04 models the H6 and H4 axles are interchangeable/identical. i'd imagine the same is true for 05 as well. an ebay or opposed forces or other axle look up would likely delineate that.
tried google yet on those axles? a google search would provide broader feedback across many subaru forums and more. i would start there. striking out says something too.
5 replies, which i doubt you'll get, would be statistically insignificant, anecdotal, and pale next to decades of experience and countless axle threads/discussions/problem/manufacturers regarding the best approach to %100 repeatable solutions.
"accepted wisdom" - i did only mean axles, lest one thinks I'm a "Dealer only" kind of person! i'm not! people well versed in Subaru (or any manufacturer) know when to use Subaru and when not too.
solutions already exist which have been tried, tested, verified, are easy, and even reasonably priced. parts with orders of magnitude less sample size and little to no historical record are of little use practically speaking. i get it, you want to believe the marketing bent, you hope this is a good repair, you want to make a good decision. at the same time, it's an automotively infantile question and looking for a solution for a problem that doesn't exist. a lot of people do this - come on a board with some outlier solution in their head...which may or may not work (i do this too on non-Subaru forums - surely a psychologist has studied this somewhere?! lol).
if you want to order something "new" or from a company - order from FWE in Denver, you'd get the best product available, excellent service, and be supporting a great guy who has been doing this one thing for 30 years - rebuilding Subaru axles.