Which preamp for Quicksilver mono amps?

@ihcho you could do a lot worse than your AI M3B with a lessor preamp.You have a decent unit now. Echoing @soix ’ fundamental questions about what you are trying to accomplish -or- just to satisfy curiosity itch - do share more. 

A friend had a preamp like yours, IIRC some of the later AI units were designed to be used with some of the higher gain Russian 6922s although people do try others. 

Have you already checked and tried really good 6DJ8 / 6922 dual triode tubes in your unit? What’s in there now?

Check out. Linear Tube Audio, it’s $5-6k  and takes several tube choices 

it is designed by David Berning, then further  improved upon ,Made In USA 

and sounds great.

I'm using a Herron VTSP-360 with my V-4s

I too have heard them with an Aric Audio pre and the match was amazing!

Call him, his customer service is as legendary as his tube gear.

I am not looking for any sound improvement. I have not yet thought much about matching KT mono with QS preamp, but since QS preamp is relatively cheap ($1500)

I wouldn’t bother.  Just put the $1500 towards a real future upgrade like the Spatial Raven, Aric Motherload, etc. that are on another level entirely.