tube amps 101

Rogue Audio M-120 Magnums...first rate in every way, I own a pair.

Dave

Another possibility is to keep the 4BSST and replace the preamp with a good tube preamp like a Rogue 99 Magnum. With it you can tube roll 'til you get the sound you like. I had a 99 with my 4BST and it was warm and rich yet detailed and very dynamic with the punch of the 4B; excellent detail and articulation at the extremes with a rich, smooth midrange. I finally upgraded yet again from the 99 to a McIntosh C2200 tube preamp and paired with the 4BST and the combination almost ideal. You can probably get a used 99 Magnum for about $1500.

I'd do a tubed preamp first..to test the waters, instead of putting tubes next to a Bryston pre...
I second Dave's suggestion on the Rogues, bang for your buck/entry into tubes, and cheap! Or eventually may want to look at a VTL ST85, older mb120's, or newer mb125's..
p.s. I used to have a 4BST and 3BST with a BP5 myself...blow your mind a go tubes..

Greg