Yeh i went through ASR reviews of both and seems like a90 is just made to meassure well. Though i think its just part of story. Jotunheim meassures horribly. But not sure how much that affects listening experience in reality.Well... the A90 isn't a piece of Schiit.
I'd say the main difference - besides everything - is that the Schiit hardware tends to not "measure well" - it doesn't look good in measurements of performance, where the Topping gear including the A90 tops the ASR measurement graphs.
Here are the measurements done by ASR for the Topping A90 and Schiit Headphone AMP's (no Jotunheim review on ASR found):
Topping A90 Headphone Amplifier Review
https://www.audiosciencereview.com/...-headphone-amplifier-review.13592/post-410374
Schiit Magnius Balanced Headphone Amp Review
https://www.audiosciencereview.com/...lanced-headphone-amp-review.15252/post-481766
Schiit Asgard 3 Headphone Amp & DAC
https://www.audiosciencereview.com/...-asgard-3-headphone-amp-dac.14393/post-442354
Perhaps reading the ASR A90 and Schitt Headphone Amp test results, and reading comments from ASR members will help you decide which to get
I did a bunch of searches but didn't turn up any direct comparisons for the A90 / Jotunheim, just speculation based on using the A90 vs other AMPs but not the Jotunheim,
If you are a Schiit fan perhaps you'd be happier with that sound?
Though one thing i like about a90 is the output impedance this for me will probably be a selling point. + it has 4.4mm jack.
I think i will wait for black friday or something maybe i will be lucky and it will go on sale.