Any experience with Min at Tube audio lab? Solid state vs Tube pre in general

Looking to get into tubes and thought about going the custom route. Looking at a tube pre. Anyone try a pre from him and if so how did it compare to commercial offerings?
This is for Dena terminator -> AGD HE9 -> Pass x350.8 -> Yamaha NS5k
I am happy with he9 but wonder if I can do better since I moved my HD800S off my he9 onto the end (with speaker tap cables) and the sound becomes FARRR better it was shocking. So wonder if some more performance is on the table still. Another option could be doing more pass and going with XP30/XP32 pre (but this would be much more pricey).
What do you think ?