Adequacy of Mac MC7300?

Remember that the Mac amps are unique among SS amps [ at least among the ones I have seen currently] in using a matching transformer [autoformer]. This limits current and maximum output at lower impedences while smoothing out difficult loads. I personally believe that this is the main reason why "The Mac Sound" is so controversial, it does sound different and you either like it or you don't. If you want a high current design there are ones like Krell that do double every time the impedence is halved. I know from reading other posts that some Maggie owners use Mac and are happy so it is not cut and dried.

Missing something: the Mac is output transformer coupled. Thus it can have that sort of control over the output.
A PS: Mac amps and Magnepans are not a good match anyway.
Many other good amps for Maggies, so unless you already own the MAC stuff, and really want Maggies, avoid the Maggie MAC combo.

Not all Mac amps are use the autoformers. The 7300 does, however. The MC7200 does not use them, and there are other Mac amps that do not use them, either. The 7200 puts out 200 wpc into 8 ohms, 300 wpc into 4 0hms. I personally do not like the autoformers, but Mac thinks they are great. Elizabeth gives good advice, so if you don't have the 7300, look elsewhere.