I have the aleph 2's w/pass pre. I've tried the pass labs with a couple speakers. To me the best speakers are ones which emphasize fine detail but do not have that much bass.
I found the aleph 2's sounded good, but a little dry with magnepan 1.6's. They sounded a little wimpy wiht vandersteen 3's.
Where the alephs become magical is with a fine detail dynamic speaker like the audio physic virgo, tempo, or avanti (my current speaker). I have also heard them sound terrific with proac's.
I realize that the X series is a little more power oriented, so you may have different results. I would also
check the trade shows to see who is using what with pass labs. Also, just call up the pass labs tech support. They might have some unofficial suggestions.