I don't believe the X series of pre-amps have been made, since there are no service manuals or reverse engineering attempts made in the diy community. Several people have made the Aleph P 1.7, which you can find the service manual here (r2 s/m pdf):
When it comes to solid-state the Bride of Son of Zen is very highly regarded. I haven't built it myself but have heard many praise it, just search for BOSOZ on these forums.