4K headphone + headphone amp/dac system recommendations please

Given what you’re looking for, my strategy would be to get fairly neutral headphones and pair them with a good tube amp like Quicksilver or Woo Audio where the ‘phones just pass all that tube goodness through.  I’ve got the Arya Stealths and they are very neutral with tight/quick bass and very good imaging/soundstage, and although they are quite detailed/airy up top they don’t get harsh using a Class-A solid state amp.  My take is the HE1000s might be a little more detailed up top than my Aryas, but with a tube amp this still may not be an issue, and you can buy them on Amazon and return them if they don’t work out.  If you really wanna stick with solid state I’d look at something like this Pass HPA…

https://tmraudio.com/fresh-arrivals/pass-labs-hpa-1-headphone-amplifier-nzg9/

Just some thoughts FWIW, and best of luck. 

I was most unimpressed with Sennheiser headphones I heard a couple of years ago, but I just put it down to me.  Can you elaborate a bit more, please?

HD800 sounds sterile, dry, lean, bright & uninvolving to me. HD600 and 650 are musical and warm (less so for HD600). HD800 is technically better (more detailed) than HD6**, but not by much - and the latter are far more musical. Furthermore, electrostats spank HD800 in detail & low distortion, plus they’re more musical to boot. So I never "got" where this headphone fits in. 

I was looking forward to Sennheiser’s long anticipated successor to HD650, and when I heard HD800 it was like a cold wet blanket. Adding insult to injury, its design was a shameless & blatant ripoff of Sony’s prior SA3000, SA5000, and Qualia 010 models. Those Sonys were TRULY a novel design upon release, but quickly ended as commercial failures (utterly). However flawed (and they were - weird midrange), they were also quirky & beautiful in ways the HD800 can’t touch IMO. HD800 fixed the Sonys’ midrange a bit (not all the way) and lost ALL the magic that made them special in the process - an exquisitely engineered mediocrity. Also Sony’s build quality and materials were far better (SA5000 and 010). It was especially galling that when Sennheiser released HD650 as its then new flagship (2003), they made a big deal about voicing it for warmth and natural musicality, more than its predecessor HD600. Then with HD800 they went totally the OPPOSITE direction and then some. 

The HD800S revision supposedly corrects the brightness, but I was long past the point of caring when it was released. A couple years ago I got to borrow a HD820, and its sound quality is embarrassing for its cost. Perfect example of a designer being too clever for his own good, with the concave glass windows (wtf). 

You can amp the HD800 into oblivion and get it to start sounding natural again, but you can also do this with 650 and I’ll still like its result better.

Thank you for allowing me to once again express how much I hate HD800 lol

@soix 

Thanks for your suggestions re: Aryas and Pass.  I did notice that Pass unit but as I haven’t come across any mention of it in discussions of favored amps on headphone enthusiast sites, I’ve been unsure what to think. 

You should also be considering the Auzeze planar magnetic headphones like the LCD-X or the XC if you prefer closed back. These are relatively neutral. They are similar the Sennheiser 600 series in the midrange but with real bass. But if you want something warmer in the midrange, try their  LCD-2 or LCD 3 models. I would caution that everyone’s ears are different, so you really need to listen/demo headphones. And some companies like Audeze have a 30 day return policy. They will be at Axpona and CanJam.

Here are a couple reviews of the HPA-1 that might be helpful in case you haven’t seen them already…

https://www.stereophile.com/content/pass-labs-hpa-1-headphone-amplifier

https://www.theabsolutesound.com/articles/best-headphone-amps-series-pass-labs-hpa-1-review/