The Pass X-1 is a good preamp, but i would go with the BAT 51 SE , i think it would perform a tad better overall..I have heard both and my friend owns the Pass X-250 and the BAT VK-40 and loves them..
I am a loyal Pass owner and fan. Nelson and Wayne and the guys (never leave Peter out; simply the best!) are the best, and so is a lot of the equipment thay make. But the Pass X1--I could never warm up to it. I tried and tried to like it. It's sexy looking and will no doubt run forever. But I have become a true believer in having tubes in the preamp. There is more dimensionality, dynamic excitement, and well, TUBE MAGIC that I could not get out of the X1; not even close. I love my Aleph 60 mono amps (bit of a cult item at this point), but the X1 just left me bored.
I own an Aleph 4 and I agree with the above about the Pass X seriea preamps. I also could never warm up to them. Although I tend to lean toward tubes in the preamp, there is at least one solid state preamp that I would consider and that is the Ayre K-1X. Other tube choices are CAT SL-1 and First Sound Presence Deluxe. I have heard the BAT 51 SE and I was underwhelmed. There are plenty of other good choices, I am sure, and there are many which others talk about, but I haven't heard many of them, so I'll remain mute, except on the 3 that I mentioned.
I liked what Rayhall said and would add... I have Aleph 2 monos and after looking around a lot two years ago I bought a ARC Ref 2 mkII. I run balnaced. It mates well with the 2s. Big sound stage and good dynamics. My phono pre is a Ayre P-5x. It all works well.
Full discloser, I will be replacing my 2s in the next year, which drive Vandy 5As, with something with more power. Looking for Tubes.
I'm not pushing ARC but they or something in that range of sound might be the ticket.
I do not believe the Pass 1.2 is truely a balanced amp or really benefits from balanced interconnect. I owned the Aleph 5 for years and thoroughly enjoyed it. I had the Pass X2.5 which is similar to the X1 which was excellent, but I much prefer my deHavilland Mercury SET tube preamp. See the review in Enjoy the Music.com and see my review on Audiogon and Audio Asylum. It is just plain more musically realistic sounding with no fatigue. The price is a good value at $3900 and I believe Kara or George at deHavilland will give you a 30 day audition.