I took the weekend to compare the Midgard (M), Asgard 3 (A), and Jotunheim 2 (J). I'm not too sciency so I volume matched as best as can be by phone spl reader between the ear cups, but that's as thorough as I get. Dac is a Border Patrol R2R dac that's RCA only, so no XLR inputs used on any amps. All were on high gain using a mixture of 6.3mm and XLR cables. I wanted to use XLR for the M specifically to utilize Halo as I've come to appreciate it's clarity over the hazier non-Halo output. Of course 6.3mm out of the A and for the J I just stuck with the 6.3mm output as well. Here's my notes, no order, rhyme, or reason to my madness, just by ear impressions swapping the amps. Headphones were the ZMF Atrium Closed. The isolation helps me zero in on fine differences better than the open sets I have.
First things first, I don't hear any significant differences between the amps. I'm not one to use hyperbole much, if I say there's a night and day difference, it really needs to be a universally large and identifiable difference that has a transformative effect to performance. Slight tonal shifts are not significant to me. And for the most part that's the main difference I'm getting between these amps... Tonal Differences. I'm sure my hearing will be questioned, but my older ears do not pick up huge differences between them. That doesn't mean they all sound the same, they don't, but the differences are on a smaller order of magnitude to me.
So lets start with tonal balance, as that's the #1 differentiator IMO. From warm to neutral I put them as such: A then J then M. The M is the most neutral of the bunch by a fair margin to me. It lacks any additional warmth or thickness down low. The A goes the opposite way in that it adds more meat to the bones, so to speak. There's a slight but noticeable bump to the lower regions that adds thickness and weight to the notes. The J splits the middle, being a bit more neutral than the A but warmer than the M. The A really stands out with it's warmth, it's almost tube like in that regard. If you want neutral, go with M and call it a day.
Soundstage was tough, as I'm not one to really spend much time on it. All were very good, but also different. The J was the widest by a fair margin to my ears. Left to right panning like old school 70s classic rock was really wide, sounding the farthest from my ears in a straight line. The M and A were similar in width with the M possibly wider but could have been my imagination. But depth and dimension really changed from unit to unit. The ability to place objects spatially in a 3D field is what I'm talking about. The M had the most cohesive stage of the bunch, placing objects in layers and stages better than the other two. Two instruments of similar pitch on the same plane would slightly blur and overlap on the A and J, not as much on the M. The A was next best in this regard, offering a decent spherical stage but lacking fine placement. It was like hearing performers in the dark where you can't see them, and can't quite place where exactly they are on the dark stage. The J was the least spatial to my ears, despite it's large width. When layering performers like an orchestra, it just tosses everything at you for a general direction without any pinpoint accuracy like the M gives you. Despite this, I didn't feel I was losing anything important with the J or A. But I don't put much emphasis on stage, so keep that in mind.
Another thing I don't put much emphasis on is resolution. I personally believe there's way too much focus on resolution as the be all end all criterion in audio. I put much more emphasis on tone/timbre than I do resolution. So grain of salt there dear readers, I'm a strange one for sure. In terms of raw resolution I rank them from most to least as such: M, J, and A. M and J are close, but A is a hazy beast in comparison. The M is very clear, very resolving, with highly delineated transients, and excellent separation. The J is no slouch either in terms of raw resolution. But the extra warmth it has tonally make it a bit hazier and smokier sounding, like a very very fine blanket of smoke was in the air vs crystal clear air for the M. The A is a cigar room in full swing in comparison. I personally have zero issues with it, I think it offers adequate resolution, especially for it's price. But if you're into details, the M does it best.
Treble can be problematic on solid state amps for me. I'm terribly sensitive to it and have low tolerance for sibilance. Some amps like those THX amps get my tinnitus going like you wouldn't believe. Doesn't take long either. I despise them. Another grain of salt and point of reference. So how do the Schiits do up top? Remarkably well, thankfully! Now they're getting a huge boost from that luscious R2R dac behind them, but they all benefitted equally, so it's still fair. The A is the most relaxed up top, with softer and less prominent extension up top. I don't feel like I'm missing anything, but it's definitely not bright or top heavy. The J has the most extension and is the closest to fatiguing here, IMO. The treble has great presence and can at times be slightly bothersome on really thin/bright recordings, but overall is still well behaved and not sibilant in general. The M surprised me in that it's the leanest sounding of the bunch but not the brightest. Treble presence is right there with the J but it's smoother in a way, not as harsh or hard sounding. More organic and analog, if you will. I'm very impressed with the treble of the M, it's nothing like the early gen Schiit treble that was hard and fatiguing to me. Think OG Jotunheim, Magni, etc. Those older units were really tiring to listen to. But these last models have really impressed me with their treble smoothness.
Bass goes boom, right? End of story? Kinda, honestly. They all do bass really well. The A is the boomiest, the J is the tightest, and the M is the Goldilocks, being tight enough to not be slow, but not too fast and taught to be boring. The J bass is really tight and impactful. Speed and precision were the main notes I kept jotting as I listened. The M wasn't far off, but it had a slightly more natural and analog sound to it. The A was great, but slower with more decay and resonance. I personally like that, but that's just me. I'm weird.
Random notes and thoughts.
Surprised the M is the most neutral but not fastest or brightest. That's the J.
A really sounds like a tube amp with neutral sounding tubes but without the tube holographic soundstage. For me personally the most engaging listen.
J has such powerful bass!!!! Hits like a truck! It and the Atrium closed is thunderous.
Metal Church on A mutes the high pitched vocals, listening to Anthem of the Estranged. J and M do this track justice.
Tin can death metal recordings brutal on J, only slightly better on M. Stick with A for bad metal!!!!
Why am I listening to Baby Metal? better question, why am I enjoying it? ugh take my metal card, i don't deserve it... and little Japanese girl singers are really annoying on the J. Too shrill!
The Ori fostex mod really likes the J. Sounds so powerful. M and A sound good too, but the J really moves that driver!
The HD820 and M are really good together. Some synergy there, maybe Halo in effect more than with the Atrium? From here on out notes are with HD820 unless specified.
Gotta love Fleetwood Mac on the M. Stevie's velvety voice is sexy as hell, so alluring and engaging. The M really brings the extension and presence needed to do her voice justice.
Johnny Winter's guitar sounds epic on the J. Bright yeah, but also powerful and emphatic.
After Johnny, had to pull in some Albert Collins, and... not so much on the J. But the M! Powerful and emphatic! Weird the J was not as enjoyable. A is too polite here, zzzzzzz
Goatwhore might be the greatest metal band name, period. G O A T W H O R E !!!!! give me my metal card back, beeches! Pure energy with the 820 and M.
New Metallica album harsh on J and M and 820, had to go back to the Atrium for a few of their tracks. why do they like hot mastering so much?
Want change of pace, HD560S and AR Rahman soundtracks. Really like the 560 with the A here, too bright on the others. J is smoking my ears!!! Whole album seems hot up top, too loud, irritating. Bad example but i listened, so will note it.
Whiplash soundtrack epic on the 560 and all amps. A brings a bit more bass, M the most even handed, J brings the horns. All good sounding, clear. Exceptional recording quality, probably also a bad example, but will note it.
O Zone Percussion Group oddly isn't as bassy as I remember it on the 560. Grab Atrium... yep there's the bass! Man Atrium's bass is so far ahead of the 560's . More quantity, quality, etc. Hmmmm I thought once the HD660S2 as a poor man's Atrium, lets check. Yep, still holds true! Really really enjoy the J and S2, that combo brings the percussion!
Thinking do I really need all my ZMFs with the cheap S2 sounding this good? Existential questions later, Carach Angren playing those nasty double bass blasts. EPIC!!!! The M here really stands out. Not as much quantity as the J but best quality.
OK those were almost verbatim from my notebook. No joke I write notes as stupidly as that. I only left out the swears and and extremely NSFW stuff. I don't think you want to read me noting i'd rather stick my mouse up something instead of another minute of all the generic female pop crud that is out there. And in those notes do you see any consistency? I don't for sure. That's my point, I could live with any of them happily. For the differences they do present, IMO they're just not that different enough to warrant worry over. Buy whichever calls to you. Does one have a name you really like? There you go, click buy. Want the newest toy on the block? M and be done. Want Thor's home? A and hope he doesn't smash it with his hammer. Seriously though they all do great things with minimal glaring weaknesses. If you want night and day different, get a tube amp and roll some tubes. Twist my arm and demand I grow a pair and declare a winner? Asgard 3, I like warm/fun/engaging, and of the three it's the mostest of those things.
Hope my idiocy helps some. Hopefully I didn't create more problems in your mind. Hopefully if you say I did that to you I won't pretend to be sorry while secretly laughing at you. And if you say I'm wrong about anything I wrote, I WILL CRY...
PS please don't mention the Baby Metal thing to anyone.
I've been doing headphones for 2 years, give or take. I'm still pretty fresh. 
