On another forum it's not just considered established fact that the Gungnir Multibit has received a silent Analog 2 update, but that the Bifrost Multibit also has seen a change that supposedly makes it sound significantly closer to a Gungnir Multibit (Analog 1, presumably).
Call me extreme, but to confirm burn-in as the reason for sound differences, I would buy two new units at the same time, open them up to confirm there are absolutely no visible differences (Schiit silently sold a few Yggdrasil Analog 2s at the old price before announcing the change, so it's conceivable that someone ordering two units may receive one older and one newer revision), confirm that the sound is the same initially (to account for good parts/bad parts, differences in the burn-in time at Schiit HQ, etc.), then use one for, say, 200+ hours with the other one sitting in a box, then turn the new one off and let it cool down for, say 4+ hours, then turn both units on at the same time, ideally with a Y splitter for power and identical power cables. If I then hear profound differences, going back and forth with the exact same cables, transducers, etc., I would be relatively certain it's burn-in (vs. warm up, silent revisions, parts differences, etc.)