Hi Dan,
I am a newbie but I have been reading a lot about the 1.6s and here is what I have discovered - The 1.6s do not go well with tubes (and I think Magnepan themselves say this). I have read this on many discussion boards.
Also, John Valin, a very highly respected reviewer in TAS was reviewing your A21 and at the end of the review he said something to the effect of "Oh, wow, what a magical combination this amp would be with a pair of maggies." From what I gather you can't go wrong if John Valin makes a stement like that.
I think you may be more than fine with what you have and based on my research, in fact I have a pair of 1.6s, an A21 and a Jc2 coming this week.
Anyway, you might find me on here next week asking some set-up questions when my gear arrives, but I feel pretty confident that the gear combination is right, just got some tweeking to do hopefully.
Good Luck