Magico A3 vs Magico S1 MK2

I was in this same position last summer. I was offered a demo pair of S1MKII in m-coat around the same price as the A3. The A3 sound  great but imo the S1MKII are on another level. The mids and treble are clearer with more definition than on the A3. It is more true to life and presents more of what it is given. The S1MKII also disappear alot more than the A3. There is less bass but what it is lacking can be made up for with a pair of subs.
The S1MKII is also more expensive at list price. M coat comes in at almost 10k more than the A3. I would also take a look at the new A1 with subs those speakers are pretty damn good. If you can get a pair of the s series though I would do that over the A series. They are just a more refined sound presentation. 

I know that you ordered the A3. I would say that if you can get a pair of the S1MKII for less than the A3 go with them if it is not to late. I got mine for the same price as the A3 but they are in the Mcoat finish a $4k premium. Like I said if you add a pair of subs I think that they are a much better speaker than the A3. The S1MKII is a much more refined sound signature. Yes they do require good power. I am using them with a Hegel H360 and they sound incredible.

I would look into a new amp you will want more power than what the naim has on tap imo.