I agree with the post mentioning different tubes. I find Amperex Bugle boys to add a little bit of "tubeyness" to the SF preamps, as they are generally very neutral sounding. You wouldn't have to change all of the tubes. I recommend these be placed in your cd player first. The Parts Connexion might have some insight on this. I also agree with Sean's post as well.
Sonic Frontiers or Pass with Dunlavy 4a
Heres my situation. I have a Sonic Frontiers Line 3 preamp connected to an X-350. I have an opportunity to go with an all Sonic Frontiers system, Power 2 and SFCD-1 and I like the idea of trying components that were made to complement each other. On the other hand, I could go for the X-1 preamp. I like the natural, detailed sound of the 350 and i've heard the SF tube amps are on the neutral, detailed side as well. I would like a little more bloom in the mids but not at the expense of sacrificing everything else. Im not trying to turn this into a tubes vs ss thread, but I wouldn't mind hearing from people who have had both driving their Dunlavys. Im sure opinions are extreme in both camps and thats fine, i'm just trying to get some insight before I make a decision. I also have a concern about the power 2's ability to drive the 4a's.