I got a few hours of listening in yesterday, with a signal chain of Spotify HQ --> LG V30 Quad DAC --> THX 789. Wide range of music all across the spectrum... RHCP (Dark Necessities FTW), 21 Pilots, Eagles, Disturbed, Kanye, Tech N9ne, Mick Gordon, Celldweller, Flaw, Beethoven string quartets, Garbage... you get the point.
TL : DR - I am pleasantly surprised; this headphone delivers for those interested in a balanced, neutral, 'true to the recording' sound while still giving it a sense of life. It could have a place in my headphone stable and if I decide to keep it the DT1990 may be the odd man out. Sound quality is more than good enough to compete at this price point.
I had zero expectations and came away pretty pleased. Negatives first though. It creaks a bit and the cable can be very microphonic, which are things I've not really noticed on my other headphones. I also have no real idea what the difference in their 2 cables are - both are 3.5mm terminations for the source hook-in but one cable has a single heapdhone-side termination and the other has 2. I know the headphones are wired in parallel and there isn't anything I could see in their documentation, sooooo... alrighty.
Sonically I really have no complaints. It is designed to be neutral and in that way it delivers. With respect to out-of-the-box performance bassheads won't be satisfied, trebleheads won't be satisfied, HD6X0 disciples may not feel the mids are adequately violating their brainspace, and folks looking to feel like they're listening in the openness of a Kansas prairie may find it closed in. These do take some EQ though and can do a bit of chameleon-acting if one is so inclined.
Soundstage is a bit more closed-in than my HE-500s but the tonality does strike me as even more neutral. Has a Goldilocks presentation in that, to my ears, everything is 'just right'. I perceive the music to be giving me what is there, as it is there. If hard-hitting bass (Celldweller, rap) the headphones slams; if layered and spacious (Dark Necessities) I hear layers and space; if strong vocals and thick mids (The Score) I get thickness; if mastered to win the loudness wars then my ears are assaulted.
Bass seems fairly well extended and stays clean with things like Love Lockdown, which makes a lot of headphones distort on that lowest hit. No hint of bleed into the mids. Mids are even and as full and textured as the recording calls for, with male and female voices alike sitting right where they are in their respective mix. Treble is as bright as the recording with perhaps a roll-off at the uppermost range, and this delivers good detail without feeling artificial. Separation is satisfying.
Going between these and the DT-1990s reveals the slight brittleness that I've come to recognize in the 1990 treble. 1990 hits harder though. The HE-500 has an ethereal, smooth quality in the mids and overall presentation that isn't in the Avantone but that's fine since I don't think Avantone was going for that.
Given I've only had a few hours to listen this post is already longer than I intended. I may come back in a week or more with some more specific thoughts. Until then I bet buyers will continue to be pleased with this headphone.