I have both HPA1 and LTA MZ3 as preamp to XA25. They are both great choices and there are reviews describing the pair online.
Exploring Preamp options for the Pass XA25
Please feel free to share preamp options for the XA25. I presently have an Acoustic Research LS-3 and am not sure this is the perfect combination. The Pass Headphone preamp is one option that I'm considering. Tube preamps?