Tube Amp or Tube Pre Amp

Yes......What is your budget? (add more!)  300B push-pull amps hard to beat. 

Maybe first add a pair of subs to yr. Cornwalls. As others have said maybe a speaker upgrade but the subs w/ the Cornwalls would be a whole new ballgame.

Some great brands Lamm, Spatial Audio lab, Triode, Air Tight and Shindo come to mind. (Spatial fan and user)

Also some great integrateds can be had.

Re: Primaluna EVO 400 Pre for Cornwalls. It should be noted that the rectifier tubes are late 50s Holland made Mullard GZ34’s with the metal base. A pair of these will set you back but well worth it in my experience. Also, the two gain tubes are vintage Amperex "Bugle Boy" 12au7’s. This combination of tubes takes the Primaluna to a whole new place. It can take any preamp set up for these tube categories to a whole new place.

Thanks everyone for your suggestions. I would like to be around 5k for the preamp so was thinking maybe a used Mac Mc 2700.  I’m mostly streaming so a built in dac is preferred, 

Check out the BHK series preamp and amps from PS Audio.  Both are Hybrid with tube front ends, so you can roll tubes til you find a combination that you love.