Crucial TUBE question

"Yes, called super rectifier, they do make a huge difference for some reasons I understand and some I don't."

Well, basically, you're fiddling with both the amount of HV voltage fed to the mother unit (which will change the operating points of the tubes in that unit), and with the impedance of the power supply itself, along with whatever colorations result from the choice of rectifier tubes.  

If it was just amount of HV, then why does the sound change even if go from 2 866a tubes to 2 3B28 tubes, same voltage drop. I don’t think voltage drop is a problem in a preamp or Dac, the drop in voltage of an 5ar4 is 17 volts, but that’s not going to happen until higher current.

Like I said, it's a combination of factors.  One way or the other, different rectifier tubes will impart a different sound to the amp or preamp.  A lot of technically-minded folks will disagree with that, but I've always found it to be the case.

Lots to digest here.  I’m impressed by the depth of knowledge you all bring to this area of audiophilia, and I’m learning a ton.  I will try to tread more carefully and when in doubt—-I won’t without running it by folks with experience.  Thanks to all for helping me better understand how to avoid stepping on my own tail.