Tim1, if Mac has output impedance of 250Ohms, the 40KOhms input of 201 will accommodate it quite well.
The 501 monos, Continuum 500, and 312 all contains the same underlying 1000ASP modules and yield the same nominal power of 500W with a max 45A current. Having said that, the devices' designs are increasingly sophisticated as you move up in price. I have published a brief discussion of the JRDG 312 on issue 188 of TAS, I believe around page 80.
The 201 and Continuum 250 are instead designed around the 500ASP modules. Unfortunately I do not know too much about 201 and 501 internals, but I can tell you that the 501 yields a much more full bodied and authoritative sound than the 201s. None of these 3 devices contain the internal PFC rectifier that give the C500 and 312 their magic, but they do accept external units to bridge some of the gap.