Need a tube power amp to go with Sonic Frontiers SFL-1 Signature hybrid pre-amp

This @kwoksun 

Using a pair of Quicksilver Mid Monos with a SFP 1 , sounds great.  

VTA amps for tubes4hifi.com

Sonic Frontiers Power One.

Chris Johnson at Parts Connexion can help you out. He was the founder of Sonic Frontiers, and Parts Connexion is in Hamilton, Ontario.

You could look for a Sonic Frontiers amp on the used market. That would be a nice matching set up. 

Just remember the SL6's are notoriously inefficient and dip well into the 4ohm or less area.  I have a set as well and drive them ok with a 40wpc SS vintage amp if you keep the volume reasonable you should be fine. But I believe they are 82db 4ohm rated so take note.

My vote is for a McIntosh MC275. Used, it should be within your budget. I had a MkII, the Gordon Gow Commemorative edition for over 20 years and at 75 WPC (though routinely measures at 90 WPC) drove various pairs of Martin-Logan electrostats with aplomb, including the CLS which dips to near one ohm in the top octaves.  I attribute this to the very low, for a tube amp, output impedance of the Mac as I detected no roll off in the high frequencies.  Holds its value better than most any other tube amp and made in the USA.  Very easy on tubes, too!