I have heard both preamps and I came to the conclusion that a recapped FET 10 HL sounded nicer to my ears.
It had a bloom bottom end, rounder, better extended base I imagine to hear from live concerts. The midbass was clearer and more foward than with the BHK. Also, the top end seem to be rendered more softly with the BHK, however, to my point of view detail was missing and it was too soft and not present enough.
On the Threshold the top end is a little sharper and more intense than with the BHK, but after recapping it didn’t not bother me. I loved the detail and the seperation of the instruments that were better than with the BHK.
Well, now you can blame me for using a solid state device before a tube unit, but well, it sounded more real to me.