Conrad Johnson--Best used Model

Used to own a 17LS2. I rank it as the 2nd best preamp I ever owned

Pass amps tend to sound best through their balanced inputs. c-j only makes single ended outputs. Some of the c-j pres  output impedances might be tricky with the Pass's input impedance.

Buy a used Pass Labs X1 or XP15 from Reno Hi-Fi.

CJ is a poor match with Pass, IMO.

Unsound is right, Pass is best with balanced.

Hey not what you specifically asked but when I had that amp in my system it really sang with a Lamm LL2.1 Deluxe and prior LL2 Deluxe, this pairing was the best I heard the XA30.5, if the amp wasn't 80 pounds and bulky I would still own it and kind of wish I still did.

The CJ is very good.  I had the 17LS. That being said, I'd look at a balanced preamp from BAT or Cary to go with the balanced Pass.  You have to be privey of the output impedence of the pre with the input impedence of the amp.  Best.  Regards......