I have compared the LS-25 MKII to the Ref MKII. The Ref was more lush in the mids, more extended in frequency and more musical overall, but at the list price, a lot of $$$ for a little more improvement. The CJ LS-17 MKII ( the one that is around $4-$5K ) was not as detailed as the LS-25 MKII but had a more lush mid range, more tube sound with more rounded bass notes, etc. Combine both and you'd have a great preamp. There are several tube preamps that I would personally like to try, the H-Cat with the newer features, the First Sound (just check out the volume control in one of these units. As for used components, the ARC LS-5 (I think that is the one most prefer), Counterpoint SA-5 & SA-5000, Sonic Frontiers model 3 and Aud Ill 3A. The AI 3As go for a song used and with NOS tubes are a great bang for the buck.
Happy Listening.