Got to jump in here. I own the Pass Labs X-150 amp(not the .5). I think "lean and cold, very much like stereotipical SS amps" is a bit harsh, but I understand what the previous response was trying to say. The X series is a little on the lean side through the mids, but it is not cold sounding to my ears. I have compared this mp to an older CJ amp, and while the CJ amp is much warmer and tube like it is not in the same league. I have had many amps in my system including some hybrids. The Pass amp has been my favorite. I have also heard the Aleph series, and while it is more natural and tube like through the mids it is not as extended on both ends and not as dynamic. I don't doubt the .5 series bridges the best of the original X series with the Aleph series if you can play in that price range, I'd go for a .5 series (or better yet a XA.5 series - real big $$$). I think the original X series sound great when mated to a warm sounding preamp that can drive the lower impedance of this amp. Happy hunting.
