Hey Richard,
The B200S is a good match up with any rack mount preamp regardless of brand name, because it's the only one that amplifies cleanly, and doesn't sound like a solid state power amp doing it. I would say it's more of a Hi-fi type of amplifier for guitar.
That isn't what I'm looking for in this case because I already know what that's like. My Strats do sing with that setup and it's a good sound, don't get me wrong, but I want to see the pre amp drive the power amp in the front end a bit harder. With the ADA power amps, all my overdrive is coming from the preamp.
I could be wrong about this, and MJMP will correct me if I am, but I believe the Marshall preamps are a weaker output than the ADA's, (based on my experimenting with the JMP-1), and I believe the ADA will drive a Marshall power amp harder the way I'm looking for.
As for the Mesa power amps, I'm wondering if this would work this way too? The Simul-class power amps might do this from what I'm reading about them since they are running a Class A, and Class A/B poweramp at the same time. I know Class A are the old smaller combo amp designs that did overdrive easily but at low wattage, by running the tubes hotter. Class A/B runs the tubes cooler, but more efficiently, and produce higher wattage. Running the two poweramps together the way they describe, sounds interesting, but I can't seem to come up with an audio reference that would give me an idea what that might sound like. It could sound really good, or it could sound like a train wreck for all I know.
The Mesa 20/20 and 50/50 poweramps sound like they would amplify much like the ADA SS amps, but with tube fidelity, but I could be wrong about this too.
Harley