Went ahead and ordered the Element IV.
I've now gone from the Atom Amp+, to the Atom Amp 2 (I wanted a 4.4mm output mainly for convenience since it makes sense to use 4.4mm for portable devices and at the time didn't see an adapter that wasn't unnecessarily expensive: oops, Hart Audio sells them for like $20), and now an Element IV.
It's not all JDS! I also have a Little Dot Mk ii and a Gremlin on the desktop side, and Qudelix 5K, Fiio KA17 and Hiby R4 on the portable side (the 5K and R4 are distinguished by excellent EQ functionality; a trend shared in common with the Element).
As a He6se owner, i was a little disappointed there isn't a bigger jump in power from previous models and the Atom 2, though in my experience the Atom Amp 2 can drive the He6se just fine (with some EQ too). Could it be driven better? Perhaps. I don't have a more powerful amp to compare against.
As I see it the benefits I'll get from the Element IV are:
Form factor - small, sleek all in one
No messing with gain adjustment - not much of an issue on the Atom 2, given low gain is already enough power
Perfect channel balance - this is an ACTUAL benefit because, while the Atom products have hade excellent channel matching in my experience, you're still limited in what you can drive with usable volume range without also adjusting the Windows volume. Just leaving Windows volume alone and doing all volume control with the Element is a subtle but potentially massive improvement in usability when driving sensitive headphones.
Bit perfect EQ - does using Peace and resampling most audio through Windows actually degrade sound quality? I tend to doubt it. But if you're like me, you'd rather just have bit perfect audio and not worry about it.
System level EQ - Meaning the EQ profiles exist within the Atom and will apply when used with other devices. It hadn't occurred to me until I started writing the post, but the Element IV actually solves a problem for me: desktop listening while WFH (with a work laptop I don't use for anything personal).
With the Element IV and Synapse, I can actually easily swap between my desktop PC connection and my phone or DAP, while retaining EQ and without putting stress on the USB-C connection (because of the Synapse go-between).
What are the cons?
Limited IO
Not the most power
That's about it, if it delivers. Based on prior experience with JDS, I expect it will.