Which preamp to go with pass labs x150.8

a REF5 or better yet an SE is a formidable preamp…. of course, i am biased….i have 5K hours of happy listening in w mine…..

Best to you and good luck on your musical journey

…but an Ayre KX-R is fantastic also…. RIP Charlie

I do not suggest a tube preamp with any SS amplifier,as it is not a good match.
 

There are many including myself that would strongly disagree with this!

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

I owned an Audio Research Reference 5SE for nearly ten years… marvelous preamp.  If I had not upgraded the rest of my system and in the process my ARC to REF6se, I would still be very happy with it. For much of that time I had a Pass x350. A very happy combination.