Forgive me for not responding to the question you posed ("ARC LS25 or Pass Labs X1??"), but consider the following:
I had to sell a CAT Mk. III preamp because of its high gain which, combined with the sensitive inputs of my VAC Renaissance 140/140 Mk. III monoblocks, likewise gave me no play in the volume control. I have since had a Hovland HP-100 preamp and currently use a Rowland Coherence II preamp, both mating very well sonically with the VAC amps. Both have much lower gain than the CAT (which has nearly 30 db. of gain). The Hovland had no remote. The Rowland has 99 volume steps, a good remote control and gives all the control over volume one would ever want. Rowland's Synergy IIi preamp is close in performance to the Coherence II and can be had for roughly $3k used. Both Rowland preamps are true, fully-differential balanced designs (they feature balanced inputs and outputs only).
Because I believe that the differences in sound between good preamps tend to be subtle (with, very generally speaking, tube designs having an advantage in soundstaging and solid-state designs being more quiet), perhaps you would want to widen your list of potential candidates. In this regard, you may wish to add the Rowland Synergy IIi to your list (as far as fully balanced preamps go, it is certainly a major player).
PS - I have owned an ARC LS-3 preamp for ten years (it still anchors my second system).
I had to sell a CAT Mk. III preamp because of its high gain which, combined with the sensitive inputs of my VAC Renaissance 140/140 Mk. III monoblocks, likewise gave me no play in the volume control. I have since had a Hovland HP-100 preamp and currently use a Rowland Coherence II preamp, both mating very well sonically with the VAC amps. Both have much lower gain than the CAT (which has nearly 30 db. of gain). The Hovland had no remote. The Rowland has 99 volume steps, a good remote control and gives all the control over volume one would ever want. Rowland's Synergy IIi preamp is close in performance to the Coherence II and can be had for roughly $3k used. Both Rowland preamps are true, fully-differential balanced designs (they feature balanced inputs and outputs only).
Because I believe that the differences in sound between good preamps tend to be subtle (with, very generally speaking, tube designs having an advantage in soundstaging and solid-state designs being more quiet), perhaps you would want to widen your list of potential candidates. In this regard, you may wish to add the Rowland Synergy IIi to your list (as far as fully balanced preamps go, it is certainly a major player).
PS - I have owned an ARC LS-3 preamp for ten years (it still anchors my second system).