If you like the Mac sound, don't hesitate to buy it. It will last you a lifetime and you always have the abiity to sell it rather easily given its high resale value and current demand. I have heard the 501's and 1.2Ks and they are very good amps. I have owned my MAC pre-amp (C-29)for 27 years and had it in the shop once. Its like my honda with 225k miles on it, all it does is start up every morning! Dependability at its best.
With that said, while the Mac does many things well (coherent,dynamic, imaging,warm,musical), it is not the most transparent,resolute or fastest amp out there. Images tend to be a little farther back from the soundstage (could be a positive or negative).
The bottom line is do you like the Mac sound?
If you do, you are buying a very well built and dependable amp backed by a company that has been around a long time. If you don't, then it doesn't matter how well it's made.
I hope that helps
