best pre -amp under 4000$

What power amp?
Assuming tubes, I would look at Juicy Music Peach, on the cheaper end, or Shindo Aurieges-L, on the higher end. Solid state, i have heard great things about the Parasound JC1.

DODD AUDIO - battery powered/tube pre.
Supratek
Audio Analogue Bellini preamplifier - Battery power supply - $3,500 retail - Sell $2,800 from Response Audio
Modwright 36.5

All great preamps

I am sure others can recommend other great choices.
These are my personal favorites within your budget new or used.

RWA Isabella is great but the DAC option is a must to get the best bang for the buck. That option would put that preamp/DAC out of your price range tho. It must be heard to really appreciate the innovative approach and sound qualities. It is possible with 30-days money back guaranty.

Good luck on your quest

Mariusz

Coda