When it comes to ampification - looking on Magnepans FAQ - there is no advice on wattage - just the amps ability to drive speakers down to 2 Ohm - and the simple and low cost NAD amps can do this (I have a NAD 325bee which falls into that category easily).
In addition to the low priced but competently designed NAD (no amp exotica needed here), I also own the Yamaha AS801 and a Croft 7 power amp. The latter Croft does not seem to fall in line being a lower powered amp, but the Croft has been designed to work well with Quad 57s and it did drive a pair of MG-1s I tried many years back very well.
And thanks for recommending the MG12.