Pass x600 vs. mcintosh 501 monos

Does anybody know anything about these 2 sets of mono blocks?What are the major differences in sonics with these amps?....
I have the X600s, and I like them. I find them powerful and neutral, with good extension at both frequency extremes. Notably, the highs are nice and detailed -- feathery. As Class A circuits, they consume quite a bit of wattage and run pretty hot. While their Class A architecture suppports a very smooth midrange with no trace of solid state graininess, they may not have the ultimate liquidity of subsequent Pass models in the XA and X.5 series (nor the Aleph series). Sorry, I have no experience with the Mac 501s.
Spaz, I own the Mac 501's and have been trying different amps in my system for some time now and the end result is the Mac's have stayed. These amps are a real bargain, I really like them.

BUT I just recently got a pair of PASS X600.5's and have to say that they are superior in every way in my system which involves "sound and stage presence". Don't forget that there is a huge difference in cost between these two but I have tried other amps costing even more and over all the Mac's stayed until now.

I have not heard the X600's so I can not comment, I do want to try the XA100.5's and if they don't work then the XA160.5's in my system. I heard the XA100.5's compared to X350.5's at a dealers in the same system and I preferred the XA100.5's, they were hooked-up with SWAN speakers.

Some other amps on my short list, Lamm and Cat.