New Preamp Suggestion

A friend of mine is running a pair of Revel Salon 2's with a pair of Classe CA-M600 amps. His current preamp (Pass XP-10) is likely going to be traded. He wants to find a preamp that will give him the following:

1. Better instrument separation
2. More air around vocals and instruments
3. Tighter bass control
4. Deeper soundstage

Budget is $8000ish

Thoughts?

I was thinking a used ARC REF 5SE, but a better suggestion might be the Cary SLP-05. Obviously there are lots of great preamps out there. BAT, CJ, etc.

Thanks!