Which preamp to go with pass labs x150.8

For Passlabs  branded preamp, I would look at Xp-22 or higher. Passlabs amplifiers are already dark sounding, so I would recommend matching them with the most transparent preamp you can afford. You already have a relatively smooth sound with the pass lab amps, so I would recommend matching it with a solid state preamp rather than tube, otherwise you risk losing details and dynamics