I should note that I find the BHK pre a wonderful component, headphone issue notwithstanding. It replaced a very fine Audible Illusions L3A linestage. Synergy with BHK 300s, Modwright Oppo Sonica DAC and Focal Kanta 3s is amazing.
Any thoughts on the modded OPPO as compared with Direct Stream DAC? Streaming ROON though Fidelizer Nimitra Signature server.
I have Focal Elears. I don’t use headphones very often but when I do, I’m always impressed with the sound when matched up to my BHK preamp.
I also have a Schiit tube hp amp that doesn’t sound nearly as good as the BHK.
I have both Focal Utopia and LCD-4. I like the LCD-4 better. They have a little more bottom end but are also a bit heavier.
LCD-3 here, sound good with the BHK once the headphone section has burned in.
I wish I could try my Stax on it. 
I think the LCD-3 and the LCD-4 probably sound alike. I bought the -4 just so I didn’t have a set of -3’s that I thought would need to be upgraded. 
I think the LCD’s were used in the development of the BHK HP amp.
I hadn’t heard that the LCDs were part of the BHK development - that’s very interesting.
I think the -3s and the -4s are a bit different and perhaps complimentary. To my ears the -3s are less detailed than the -4s but also less clinical/sharp. All depends on what the listener is looking for of course. 
And possibly the remaining credit card balance 
It was mentioned somewhere earlier (this thread?) that it was the Audeze model LCD-X headphones that were used in voicing the BHK Signature Preamp headphone circuit.
I knew it was one of the LCD’s. Roon also has a filter for each of the LCD series of headphones.
It helps to my ears but if you forget to turn it off and go back to speakers you will think your speakers are broken.
Update: Made settings changes to AntiMode Dual Core. HD800S now fully rock with the BHK pre. Volume is way more than adequate and SQ is outstanding.
BHK PRE - Focal Utopia w /(4m) Nordost Heimdal HP cable.
I use my BHK Pre with Audeze LCD MX-4 and the Focal Utopia with Kimber Axios AG. I prefer the Focal Utopia.
I use Utopia’s but I prefer my Woo WA5-LE fed by my BHK Pre. Nothing beats a two chassis 70 lb total 300b tube amp.