Preamp suggestion for Quicksilver M120 amps

FYI: There are two models of that QS. The older one uses 12AX7 tubes and the newer one uses 12AT7 tubes. Are you sure that the one you have is the newer one? BTW, the new model has no mono switch!

No mono switch, only power and tape bypass switches. Looks exactly like the one on QS website.

OK, I have a response from the seller I got the QS from. The unit may be not broken in. Do I leave it on for 24hrs? What is the best fastest way to get it done?

I doubt very much that will improve it. It’s just not your cup of tea. See if you can return it!

@agranttz 
Same scenario here on a 2019 Agon thread worth reading. It was a new QS linestage with no time on coupling caps or stock tubes.  Reported improvements over time from 20 to 200hrs. Then swapping out the stock lean sounding lower model JJ tubes with better vintage tubes.  

https://forum.audiogon.com/discussions/new-preamp-arrived?sort_order=asc