Nait XS with Magneplanar 1.6?

I would say 'yes too weak'. The key figure is that the 4 ohm power is no where near double the 8 ohm. A sign of a weak power supply not really meant for a 4 ohm load.
Now I have a Forte' 4a with 50 watts into 8 ohms, and 100 into 4 ohms and the Forte'4a is noted for being a high current amp.
When you look for an amp for the Magnepans, watch for the doubling of watts into 4 ohms and those usually are high current amps. And what you want for your Maggies is a high current amp, even if it is only 50 or 60 watts into 8 ohms.
I own a pair of Maggies, 3.6's with a Bryston 4B-SST2 amp (I tried the Forte'4a with the 3.6 speakers and it was fine at moderate volumes.)
The Nait is gonna sound like it is struggling, or not in control...

Elizabeth is right but don't trust manufactures specs. They sometimes (often) lie, or do not tell the whole truth. When the say an amp delivers 50w into 8 ohm and 100w into 4 ohm. They don't really lie but more often then not the 8 ohm power delivery is more then number they give you. Just so that it looks like it gives double power into 4 ohm. So when they say 50w 8 Ohm it can also be 55 or 65 w into 4 ohm and 100w into 4 Ohm.

ok. any other possible pairings with Magneplanar? I listen mainly to classical.

thanks for your advise

Nait XS punches above weight class but to get the best out of maggies you need more power. At least a nap 250 if staying with Naim.