I experimented with a number of preamps over the last fifty years and have kept coming back to Audio Research. While there was a bit of variation with the introduction of the ARC Ref 1 & 2 preamp. Once that was ironed out, in general the sound improves with each generation of preamp. The current models are spectacular… LS28SE… which a friend of mine purchased about a year ago and the Reference 6SE which I own.
ARC continues to carefully walk the line of musical first… not loosing the natural midrange bloom, then adding detail and dynamics while lowering the noise floor. Worth the marginal improvement, to me, absolutely. There are a few folks that liked the warmth… with somewhat lower detail of some older ones. But for most tastes… current are just plain better.