You might be able to find a used Carver c-19 tube preamp in your price range. The Carver C-16 solid state will be a good choice for you also. I currently own both of these preamps, but I am not using either of them right now (they are not for sale). Both of them have tone controls. At one time, they served as my main preamps with my Kappa 9's and performed well for the money spent and no bright sound.
I currently use the Kappa 9's with an Audio Research Ref 2 Mk2 preamp and Carver Silver 9t monoblocs and there is none of the bright sound you are experiencing.