A few days ago I had the chance to make a home demo of the Aries Cerat Heléne DAC, which I compared to my Chord stack.

My current digital front-end is a relatively complex chain where a Sablon Evo USB cable feeds a SRC*DX, which goes 2xBNC to the M Scaler (on battery), which in turn is connected to the DAVE via the OPTO*DX optical decoupler (on batteries) and 2xAudioquest Diamond cables. To add to the madness, I also use the DC*BLOCK units at the DAVE BNC inputs. I built this chain ("mDAVE" hereafter) over the last 4+ years and I consider every complication as additive towards a better sound.
I listen 90% to acoustic music and attend live unplugged performances on a regular basis, so to me 'better means' - subjectively - more 'natural'.
I started the comparison with the Heléne by using my trusted vintage Spendor LS3/5A, then I moved to headphones, which remain my most relevant configuration in terms of head-time.
The mDAVE and Heléne are very different sounding DACs: while being very good at everything they actually excel at complementary things.
Where the mDAVE truly shines is - to my ears - at producing holographic, transparent soundscapes, with tactile localization and flawless musical images separation. The other strongest area of performance is timing and flow: the rythmic drive is precise and propulsive, engaging and effortless.
The Heléne more impressive features are - on the other hand - tonal density, weight and timbre realism. Especially in the lower midrange / upper bass region.
Imaging is more diffuse with the Aries Cerat, it fills the room with larger / deeper sonic boundaries. mDAVE, on the other hand, has superior clarity and microdetails.
Take as an example The Ballad of Bill Hubbard, from R. Waters' Amused to Death.
This is an audiophile treat, and a great track to show off your high-end 2-channel rig to your friends if you so desire.
The infamous dog bark at the beginning of the track is more apparently even behind your shoulder (LOL) with the DAVE, and the subsequent atmosphere of special effects which creates an immersive 360° 3D bubble all around you is truly magical with the Chord stack. However, when the electric guitar plucks kick in (1:07''), the wave of warmth, the amber timbre from the Heléne are moving. When the big feline roars at 2:19'', DAVE makes you think to your cat, while the Heléne displays a puma.

Piano has a richer tonal palette and a more satisfying dynamics and resonant structure via the Heléne, with a more realistic decay. The lightfooted pace from the mDAVE wins in terms of percussive attack speed, and complex passages articulation readability, but I would give piano experience to the Heléne overall.

The same goes with strings. I listened to several quartets, solo violin / cello tracks and chamber music pieces, and the Heléne gave consistently the impression of a more accurate reproduction of the timbre, the feeling of the gut strings you clearly get in the real world was more obvious, whereas the mDAVE presented a certain metallic character which felt comparatively a bit out of place.

Instrument separation and 3D layering was instead superior with the mDAVE. You can identify in space each musician in an almost spooky way.
All in all, if I had to choose based on my 2-channel listening session, in my system, the Heléne would be overall my preference, to the point that I was actually considering to buy it on the spot. The authority and boldness it provided to my LS3/5a was unheard of in my room.
Then I moved to headphones.
Here the comparison ended pretty quickly: the mDAVE crossfeed, of which I am totally fond to the point of a true addiction, was dearly missing when I tried the Heléne.
I find many albums unlistenable without crossfeed now, and the mDAVE capability to do crossfeed right (i.e. with minimal loss of transparency) is alone worth having this DAC for headphones.
The Waters album mentioned above showed some decent level of 3D magic with the mDAVE and crossfeed (although much, much less enjoyable than the 2ch experience), which was totally lost with the Heléne and no crossfeed. I tried Roon crossfeed and I was only partially successful (maybe I should experiment more with it, but it does not look so promising).
With album requiring no crossfeed, and more specifically with binaural recordings, I definitely preferred the Heléne in combination to the AB-1266, whereas with the Valkyria the Heléne provided a bit too much of a good thing, ending up to an overly thick, mid-centric tonal balance.

Back to sheer technicalities, the bass control of the Abyss from the mDAVE was immaculate, with a clean, extended, tight presentation, whereas the Heléne was more on the voluptuous side.
Very crowded orchestral passages were easier to follow with the mDAVE, more like a wall-of-sound with the Helene.
Vocals are way more incarnated with the Heléne , but the very minute details about breathing, lips / mouth movements are best rendered by the mDAVE.
The spacious, holographic character of the mDAVE, its ability to present details in a natural manner, and the peerless implementation of the crossfeed make it very hard to beat as an holistic headphones listening machine indeed.
So for now I let the Heléne go back to the dealer, not without a touch of sadness.