Anyway reporting back on the 12bz7. Listening now with CSN on the table, the one with Darkstar on it.
So, SP-8 uses it tubes in series so the BZ is second in line, similar to 12bh7 in the M120. The whole path is sp-8 (12ax7 phono 12au7 line) to m120s (12au7 to 12bh7 to kt120).
Only change is second 12ax7 position.
With my best 12ax7, Sylvania made for The Fisher, oh hell yes.
With 12bz7, more umph, more volume (a surprise), loss of some detail in bass I think. Still pretty dang good.
With RCA 12ax7 blackplate, detail back but so is the "in your face" feeling I get from these. Kinda annoying.
So there you have it. I'll keep the BZ in for a while. It's all fun.