One main reason these solid state macs sound so good is because the circuit was centered around having a HiFi, dementional tube-like "tone" in a SS package. They also used huge and awesome tranny's. It also has an autoformer which contirbutes to its unique smooth tone. The components in the circuit are audiophile top notch from that era, all made in the USA. I am sure it can be copied, but without the oldschool iron in the trannys, its not the same.
Amps today are made fast, with cheap components and loaded with other circuits that may or may not affect the tone. Adding in buffers, tone stacks, circuit protections, limiting, roll offs, power and signal protections all add to the behavior of the amp itself. The mac is almost so primative, but perfect, that it behaives like a tube amp in a combo... the more signal you throw at it, the more you push it, the more you push it, the more harmonic it becomes. Thats why some opt to remove the mac's protection circuits on the larger, more expensive models.