Krell amps with tubed pre-amps


Suggestions and/or experiances with SS/TUBED combination. I own an FPB 200 and looking for tubed pre amp to match. ( $2000.00 used ). I know there is a minor adjustment needed inside all Krell amps if one is to match it with tubed gear. I'm not sure what specs the Krells like seeing in tubed pre amps. ie, impedence, output etc. Thanks!
alb24
Thanks for the input, Larry W., and Rmml. Is it a coincidence that both replies are using the Sonic Frontiers pre amps or is there a specific synergy with the SF and Krells that I'm not aware of. Thanks again.
I have noticed that a lot of people are using this combination. Both products are built to a very high standard , they are reliable & together they make wonderful music. Larry W.
If you can stretch you $2000 limit, you may want to try out the Hovland preamps. They are simply lush sounding that few can measure upto.
Jayt, So.. the Hovland is lush sounding?
From The Stereophile Glossary:

lush Rich-sounding and sumptuous to the point of wretched excess.