Which preamp for Quicksilver mono amps?

There is nothing wrong with the standard QS linestage or full function QS preamp, and particularly so for the price new. People like to try different preamps with different tube sets to yield different results. You might be better off trying different sources and different cables while your existing tubes are settling in more.  While it may not be needed, it's also fun to test in these other areas too fwiw. Best of luck. 

The Cary SLP-98 F1 pre was a fine system when matched to the Mini-Monos. Or for a more budget system I might want to try the QS preamp. Mike Sanders knows good sound.

I use an Audio Research SP9 pre with my Mid Monos. It's a good match. Don't have any experience with other QS gear.

I use an Audio By Van Aistine Vision RB solid state preamp with my Quicksilver Minimite tube monoblocks and they sound great together!  I paid $1000 for the preamp new a few months ago. I also ordered an AVA NP1 power amplifier which is presently being built. This amplifier has the new AVA nesting architecture that is supposed to be a significant improvement in overall clarity of the source. 

Best of luck in your search for a  preamp! 👍

Aric Audio Super 6SN7 Linestage with Mid Monos