Certainly reassuring! I'm always keeping my eyes peeled for a used pair of Aeolus. Like you said, ZMF cans really don't seem to depreciate on the used market so no fear of not being able to offload them if they're not to my liking.It does suck not being able to sample, and I realize I say this from the privileged position of having a foot in the door by owning a couple sets, but honestly if you can afford it I'd just jump on the next used one that you see. Worst case scenario you don't like it, you'll be able to recoup all of your expenses or very close to it as these things have really held their value and sell quickly. I've never had to wait more than a week to move any ZMF I've owned.
Also, I think we have different definitions of lo fi haha! I'm into plenty of the cleaner stuff you mentioned (that last Vanum record was something) but I'm referring more to things like Paysage d'Hiver, early Blut Aus Nord, Burzum and Darkthrone, etc which are all pretty incredible albums hiding under borderline offensively bad recordings. Then again, I do also agree that the shittiness of said recordings contributes to the vibe (especially Paysage).
Ultimately, perhaps barring those few examples, I don't think anything you're into would sound bad on either ZMF that you're looking at even if I'd favour the Aeolus personally.
And yes, we certainly do have different definitions of lo fi! I really dig Blut Aus Nord Halluinogen but their early releases are a bit too raw for my liking. I can appreciate the sound and the feeling they're trying to evoke with it though. The early Paysage stuff is TRULY lo fi haha. I wasn't a big black metal fan up until the past few years... I've certainly grown to appreciate the genre more and more and it's now probably my most regularly listened to metal subgenre. Vanum Ageless Fire is a fantastic album.