New Preamp Suggestion

Is he looking for tubes? What direction is he interested in moving towards? Speed and resolution OR warmth and musicality? ARC, Aesthetix and VAC are very different sounding than CJ, Cary or BAT. To make a proper recommendation it would help if we knew what direction your friend wishes to go.

Well Mike, then I would suggest he consider a preamp from VAC, ARC or Aesthetix. My choice would be to look for a used VAC Renaissance mk III, as I think that would provide the best sense of air around vocals and instruments. Very dimensional

I have also owned a ARC Ref 3, and that was a fine preamp too, so I'm sure he'd be happy with a Ref 5 SE also. The ARC may have a slight edge in bass control over the VAC. Although I haven't owned a Aesthetix Callisto Signature, I have heard one, and I would put it in the mix with VAC and ARC as far as creating a deep, detailed musical stage.

The BAT CJ and Cary models will tend to sound warmer and a bit more musical, but won't have the air and detail in the high's of the VAC, ARC and Aesthetix. The BAT probably has the most powerful bass, though I would not say it has the tightest bass control.

As always, YMMV.

@Dave_72, his friends Classe CA-M600 amps have an input impedence of 50K ohms, so he should be safe with just about any preamp.