Which Preamp for Bryston 4BST. BP-25 or Rogue 66

Also have a 4B-ST and have owned both those preamps and still have the Rogue 66. Not as detailed as the BP-25 but the tube "warmth" makes the listening hours just slip by...

I am in the same situation as yourself..looking to change from a SS BP-25 Bryston preamp to tubes.
As pointed out to me by someone in the know..you have a very good preamp amp with the BP-25 so make sure that you look for the same or better quality tubed preamp if you want to see a significant improvement.
The two tubed preamps suggested were..Rogue Audio 99 or BAT V50.(something like that)
I was very excited with the fact of changing to tubes but that statment brought me back to earth and changed my way of thinking.
So am I on the right track only looking at tubed preamps in the $2000-$3000 range and nothing less.
Sorry I didn't answer your question but hopefully we can both benefit from some further responds.

Detailed generally equals more bright.The 66 will add the warmth that makes music very enjoyable.No listner fatigue.

I have the 7B-ST's and they perform very well with a Rogue 99. I imagine the 4B and the 66 will also be a very good combo.