I have owned a number of Audio Research preamps in the last 25 years. I currently own an LS25 mk2. You should be able to pick one up used for a little over $2000. My other choice in that price range would be a LS17. ARC preamps have come a long way in the last 10 years. Far more so than their amps. Borrow an LS17 from a dealer and try it in your system. The LS17 is a stunning preamp for the price.
