I owned the Aleph P, the X1 and now the XP-20. The X1 was considerably more neutral and detailed than the Aleph P, though I loved the ergonomics of the P and the remote. The separate X1 PS also lowered the noise floor. The XP-20, though much more expensive, simply disappears. It is highly resolving of detail and nuance. It is very quiet. It is also very smooth without being soft. The sound can be "rich" if the recording is, but this is not a coloration or character trait of the preamp. I did listen to the XP-10 briefly in my system when I had the XP-20, but not for a long enough time to make an accurate assessment. After a brief A-B-A, the difference to my ears was small. More time might reveal greater differences.
If it were me, I would buy the XP-10. Of course, Pass suggests the XP-10 sounds better than the former flagship three box X0.2. You could try contacting Mark at RENO HIFI or Kent at Pass. They both know these products as well as the FW F5 and could give you another opinion. Depending on your system, you could also ask them about the FirstWatt B1 passive buffer.