Kevin,
Since your Sonatas are so efficient, why don't you just opt for a tube integrated with around 40 watts/channel or so? The Eastern Elecric E-520 and VTL IT-85 come to mind as contenders. I think you will realize the sound you are seeking better with this option than pairing the B&K amps with a tube pre. I have owned their amps in the past, and while not bad for the $$, I think the newer tube integrateds offer better sonics, especially since you don't need much power to make the Silverlines come to life.
Oz
Since your Sonatas are so efficient, why don't you just opt for a tube integrated with around 40 watts/channel or so? The Eastern Elecric E-520 and VTL IT-85 come to mind as contenders. I think you will realize the sound you are seeking better with this option than pairing the B&K amps with a tube pre. I have owned their amps in the past, and while not bad for the $$, I think the newer tube integrateds offer better sonics, especially since you don't need much power to make the Silverlines come to life.
Oz