Funny, the two amps Corey mentions at the end (Electron Kinetics Eagle 2A and PS Audio 200C) I own. The 555’s are notorious for having their power supply filter capacitors go bad (be careful about hooking one up to a pair of speakers you love), which I had happen; I don’t know if the same is true of the 535 (or 545). Anthony Cordesman (as usual attempting to get a "scoop") grossly over-rated the original 555 (dry, grainy, coarse. Okay for a sub perhaps, though not as good for that as the Eagle 2A), and was quickly put in his place by JGH and Larry Archibald.
The Eagle 2A and PS Audio 200C can be had for about the same price as a 555; both are better amplifiers.