Musical Fidelity A308 pre vs. Pass Labs x-1

My vote would go with the Pass. I've heard both and I don't think there's much of a contest, the pass just captures the subtle inner nuances of the music and it's high frequency airiness and openess I've never really heard the equal of. I use it in a Cary 306 -> Pass X-1 -> Sim W-5 -> Piega P-10 combo.
The Pass also gives you the option of going balanced in the future. The only thing the pass might miss out on compared to say the Simaudio P-5 is adding a little bit more weight to the male vocals and middle lower frequencies, but it did present a more natural and real sound in these frequencies.
Cheers

Not even a close call. The X-1 walks all over the MF preamp, really. I owned the X-1 for some time and borrowed the MF from a buddy and the Pass was way better, no contest, honest otherwise I would have bought the MF from my buddy cheap and put the extra money in the bank from the X-1. For the comparision I used the Pass X-250 amp, Kinergetics KBA-75, Graaf 5050 tube amp, and Carver Signature series II.

The Pass is more dynamic, much better bass definition and much deeper (some of the best bass from a SS preamp I have heard for the price), better separation of instruments, smoother highs and more extended, mid range was different and varried from CD to CD but overall I preferrred the Pass because it better layered the soundstage, wider and deeper soundstage.

Happy Listening.