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.