So i don't have the NX8 but i do have the AMG and it is a safer bet on design alone IMHO. That and if the NX8 doesn't have similar IQ to the ATACR then it's likely not as good as the AMG. 4x erector in a sizeable scope body versus an 8x erector with high end mag range in a compact body, There are going to be compromises by design. Now the main complaints i've seen with the NX8 are in regard to the 2.5-20x50, and while i'm sure the 4-32x50 is a little better i'm betting it suffers from distortion on the outer parameter just like the 2.5-20x50. Then there will likely be sensitive parallax and a finicky eyebox on the high end. It's just sort of the nature of using a large erector assembly in a compact scope body.
The AMG is honestly incredibly hard to beat for it's class given it's weight. There really isn't a sub 30oz optic that's FFP, Mil/Mil, locking turrets, with a quality reticle that comes close to it. It could be a little smaller yes but it is an all around fantastic optic with little to no compromises, which is why people are wanting a 4-16 or 3-18 AMG though obviously they'd have to go to a 5x or 6x erector assembly with the 3-18.
I'm curious though as you are because i was contemplating one for my 300PRC build but i need to see valid evidence from ILya or Bill that it doesn't suffer from the aforementioned drawbacks.