CJ 16ls vs Cj17ls vs Pass Labs X1

I have listened to the full CJ lineup up through the 16LS.
The answer to your question depends upon how much difference you are willing to pay for. The 17LS is the minimum I felt able to settle for in the CJ line. Once I heard it, I was only aware of what was missing in lesser CJ's. However, the 16Ls did not represent as large a step up from the 17 as the 17 was above everything else.
I have not heard the Pass Labs X1.

I'll second all that Hindemith says about the 17LS vs 16LS. I ended up buying a 17LS after auditioning both together and while I could hear the difference between them, it didn't seem to be enough to justify the additional cost. For me, the 17 represented the real sweet spot of price/performance in the CJ preamp line. However, a year ago I participated in this same thread on RAHE and several folks felt very strongly that the difference between the two was quite noticable and that the 16 well worth the addition money. Different ears, different tastes. For what its worth, I can say that I've been very happy with the 17 for the past year and a half, although I'm certain I'd also say that if I ended up buying the 16.

Unfortuntely, I've also not heard the Pass Labs preamp, so I can't provide any insights on it.

-- Ken