I also have always wanted an Audio Research Preamp (well, maybe not always, but at least since 1974 or so). I finally decide to just do it, and my used LS25 MkII arrived 2 days ago.
You don't state a cost limit, but they do make an outboard phono stage, ase well as a new SP series with a phono stage (SP-20?), so check their web site. There is also a 3rd party site listing the entire product history if you want to buy used.
I don't use records anymore so was only interested in line stages (LS-x).
Early on, they had knobs and very nice switches and ARC has always had a lot of control functionality as well as a very detailed rendering with a bit of extra mid-range (euphonic) but never a fat, bloomey sound. They have always aimed to be the best.
My LS-25 has the switches along the bottom (which all trigger relays), but the knob rotation for control is gone. Instead, you twist the knob and hold it to change volume, balance, etc. I don't like that as well, but it does get rid of the pots and their SQ problems.
The LS-26 and newer SP-x preamps have a clock to monitor tube usage, and a display panel (where the LS25 has LEDs in an arc to show volume settings, etc.)
I agree you will need to do some extensive listening to decide which has the sound you like best, as well as evaluating control functionality and the longevity of the company, since a long warranty is of no value if a co. goes out of business. Indeed, even paid repairs can be an issue.
