I've come to absolutely adore these headphones. I recently got a new cable for them from CablePro (Freedom-UPOCC cable).. whom I highly recommend (Ted offers excellent customer service and the cables are incredibly durable and well-built).
One thing I've found is that not only do they demand a very good/synergistic amp.. a HQ DAC is quite necessary, IMO, as well. The ODAC was nice.. but using it with the Uber-BiFrost & Vio V800 yield a marked improvement in sound and presentation. I've also noticed the soundstage has significantly improved since early on in my ownership. They're not HD800-level.. but the FA-002w HE's soundstage no longer sounds distinguishably narrow.. I find it much more pleasing now. I'm yet to determine if it's the cable, DAC, amp, driver break-in, some combination of the above.. or placebo.. but whatever it is, the stage is feels much more expansive than it did early on.
The treble has smoothed out.. the midrange remains incredibly transparent, detailed, vibrant, and tonally pure. Bass has excellent dynamics and texturing ability.. it's taut yet full, impactful, and nimble. The signature reminds me of a beefier, more lush RE272.. with infinitely better bass, soundstage, and dynamics. All of this is contingent on the fact you've got well matched gear up stream of it.
I can't recommend the Uber-Bifrost/BH Crack combo for this headphone enough: it's simply spectacular.. and worthy of being "end-game" for many, IMO. I feel the Crack & UB are very reasonably priced upstream components that will help bring out the best the HE has to offer w/o breaking the bank.. and they're wonderful products in their own right.
If you're using the Crack, the Tung Sol 5998 output tube is a must when it comes to hearing the soundstage quality and detail I've described. For input tube, go get the Tesla (not JJ) ECC802S. It's widely considered a near clone of the famed, stupid-expensive, and jaw-droppingly good Telefunken ECC802S... for much MUCH less ($30-$50!). I can attest to the wonderful SQ of the Tesla in the Crack (with the 5998) as I've had it for a quite a few days now and it's every bit as good as the impressions I read on them (before buying) make it out to be. It's the type of tube you drop in and will have no desire to replace, IMO... the HD800 loves it, as well.
I can't say how the HE stacks up to other (competing) full sized, closed, neutral, dynamic driver phones that have high impedance. It actually seems pretty tough to come across a phone that meets all those criteria... another reason I'm very happy to have the HE. I briefly had the (semi-closed) Beyer DT880/600 for a couple of weeks. I found it to be an excellent phone.. but felt the HE was technically superior in most all areas... most notably in resolving ability and instrument separation.
Hopefully people still take a look at this somewhat overlooked, undervalued phone.. it's getting a but tougher to find as FA seems to have shifted their focus to the Ti (which I sense, is a low impedance version of the HE.. nice.. but being able to run the HE off an OTL tube amp is part of hearing the magic, IMO), but I feel if you've got good upstream gear, this phone has the potential to know your socks off.