Which Pre-amp. match with Krell KSA 200S Pow. Amp?

Thanks for your comment.
I agree with thesoundhouse,The Krell power amplifiers to sound a bit bright,thin Mid low and a little dynamic absence!That's why I find a pre tube.
My firend suggest that I should choose Aesthetix Calypso's warm sound and good dynamic.
So, Do you think that is best choice? Who is the bestter choice, pls help me?
How about BAT tube pre? 32SE, 5i