4K headphone + headphone amp/dac system recommendations please

Thanks for your suggestions. Ideally, Id prefer to stick with SS. Can you think of any headphone/SS amp pairings that would yield "musicality with lush mids" or is that asking the impossible? 

That's a bit tougher. SS can never be as lush as tubes without becoming a dark mess overall. There are definitely SS amps that "lean" warm, and that can be a pretty nice mix with the Sennheisers I mentioned too. Certainly avoid the Gilmore Dynalo / GS designs - those are GREAT amps but they do not lean warm at all. I'm not sure what modern SS dynamic amps are good for that, these days (I moved on to e-stats). Some of the older Headroom Max amplifiers were pretty nice and leaned warm and particularly sounded amazing with the Sennheisers in balanced drive mode (for the models that had it). 

Attending a local head-fi meet or Canjam is an excellent suggestion. Like with all things audio the choice of cans and amp is very personal. Just a warning the e-stat headphones struggle more in an environment like that because they're SO open to the ambient noise, and their amps don't have reserves to just crank the volume with endless headroom like on most dynamics. 

My fav is the RAAL SR1a, but I won’t recommend that since it is a detail king. A very engaging and musical phone is the ZMF Caldera Closed. I was very surprised I liked it. I was at a mini-CanJam meet and a couple of folks there who had cost no object phone systems gave me to listen to the Caldera.

Caldera Closed LTD Walnut Burl – ZMF Headphones  ($3300)

I have a Schiit AsgardX headphone amp with the MESH DAC. It is surprisingly good (the DAC). The amp was expected to be very good since it is based on the Schiit Mjolnir 3.

Schiit Audio: Audio Products Made in USA  $549

I was planning on getting the Caldera Closed to use with my AsgadrX but decided to save cash and got the Meze 109 Pro used for $500. Since I do not listen to this bedroom system much it was a good choice.

BTW - that CanJam show in NYC had the introduction of the new Allnic ASRA DAC. I heard the $6.5 ASRA headphone amp at the min-CanJam and it was superb. I am trying to get my friend (who sells the ASRA) to convince Allnic to add preamp out from the amp so I can use it as both a preamp and headphone amp.

Well, I had a response with links and comments that disappeared into thin air. So, this will be shorter. 

Are you willing to consider used or just new? Are you set on dac/amp combo or would you consider separates?

In regards to headphones,  I second the Sennheiser HD6 family. I would also look at ZMF, specifically the Atrium Open. They also have a new planar model being released that is supposed to combine the warmth/lushness of the Atrium and the detail of the Caldera. It's called the Tessidera. You might look at the Focal Clear OG as well. 

When it  comes to amp/dac combos made in the USA there's not a lot of options. I think Schiit, which yyzsantabarbara mentioned and you own is a good option. I nearly purchased the TEAC UD-701N which is a precursor to the UD 507 you're considering. Here are a few others to consider:

1. Black Ice Audio Aries
2. Violectric DHA V226
3. Mytek Liberty DAC II
4.  ifi Pro iDSD Signature  Made in UK, but 2 offices in US
5. Rupert Neve Precision DAC

Someone on this forum (early 2025) recommended John Masseria (JM Audio Editions) as a headphone savant. Handmade and sepcifically tuned headphones based on YOUR request. And good to look at with choice of woods and finishes.

https://www.jmaudioeditions.com/closed-back-headphones

Also very well priced. Worth a chat with him to match with headphone amps / DACs.

Good luck.

Just a follow up on JM Editions

I requested cans with similar level of detail as my electrostatic speakers with tight bass. By providing him with the spec details of my headphone amp and DAC, he recommended:

XTC2 openback with 50 mm beryllium driver, 64 ohm at 101 dB efficiency, extended blissfull tuning. All of these parameters are customisable. With 3 sets of ear pads

The results were spot on.