What is a good upgrade to the Magnepan MGlc?

Yes, the IIIa is an unbelievable deal if you can find them in good shape. I am not sure if Magnepan will still rebuild them, but if they do, you basically get a new speaker for about $400. I have the 3.6r's and I think the IIIa's are in the same league with similar amplification.

1.6 are great speakers too, but they don't have near the bass response of the IIIa's.

They will still rebuild them, I started with Maggie MGIIb's and upgraded to the IIIas after awhile. I have used Audio Research M100 monoblock tubes but now use the Audio Research D400mk2 and support the maggies on the low end with a pair of velodyne 12 in. powered subs. Have kept my Audio Research SP9 mk 3 too. Still have the IIbs and they said they would rebuild them too.

Last year I pondered the 20.1s and gave them a good listen, and they did sound better in several ways than my set-up, but to me, and risking the wrath of some, it was not an HUGE improvement. Many speakers do some things better than the IIIa but for me anyway, it creates a very musical experience and except for getting a marantz 11s1 sacd player, I have quit upgrading and just keep investing in music