@aberyclark I own the BHK in a second system and have played around with it a lot. In honesty, with the right tubes it can really come alive, and has a wide, deep, 3D soundstage that most other preamps don’t have.
I compared it against an Arc Ref 6 SE like others above, but I felt the ARC to be too “lit” and did not have the warm harmonics that the BHK makes possible. It was good in other ways, but not good enough to justify replacement.
I also tried a Cary SLP-05 Ultimate, which retails for double the BHK, and the BHK easily bested it.
If Gold Lions are the best tubes you’ve tried in the BHK, you’re missing out. Did you know you can switch the current and voltage settings internally? With a proper adapter, you can use 6SN7s. My favorite is a pair of Sylvania VT-231 - really opened up the preamp in every dimension while adding dynamics and authority. There are many other great tubes, like Tungsram 7308 and Psvane T-II CV181.
Also, if you haven’t yet, try a Synergistic Research blue or orange fuse in the BHK. That makes as much or more of a difference than tube rolling.
I’ve since also purchased an Allnic L-3000 Mk 2. It, too, is an incredible preamp, but different. The Allnic is a tad bit more euphoric with the midrange bloom - it’s just gorgeous, but the soundstage isn’t as wide as the BHK. Still worth keeping at the price I got it for.
After investing in the fine tuning, the BHK isn’t going anywhere.