I have the X150 amp and thought that it may be somewhat lean in the midrange, until I changed my digital, and cables. Now, I almost think it is too rich in the midrange, but who knows. Bottom line...the amp is a chameleon and will take on the signature of your surrounding components and highlight its weaknesses. It is amazingly fast, neutral, transparent, detailed, and utterly smooth. If your system is lean, I would look elsewhere first.
For synergy, I am guessing a Pass amp is best for your X1, and run it in balanced mode. I too have done alot of research on what type of preamp to get and when I do, I will get a Pass X2.5 or if I have the cash an X1 to match my X150.