Hello, I'm running a pair of Pass Labs X600.5 monoblock amps, which, like your X150.5 amp, have an input impedance of 22kohms balanced, and a Pass labs X0.2 preamp. The output impedance of the Pass Labs XO.2 preamp is 200 ohms unbalanced & 750 ohms balanced. You could buy a Pass Labs X-1 preamp for around $2200 used or try the JR Capri preamp that everyone is talking about--(assuming the output impedance of the Capri matches). Also, depends on if you want to go solid state or tube. Sounds like you are leaning toward tubes. To narrow the playing field: First, make sure that the output impedance of your new preamp is a good match with your Pass amp. Second, try to determine if there would be a musical synergy between the two components. The second part is the harder (and fun) part. Good luck! Stan
