I agree with peppelito. The comparison is of the 2 products as is. Some are brighter than others, some are sharper than other, etc. Adding additonal equipment clouds the comparison.
A ND filter ("Neutral Density" filter) is not an "additonal equipment that clouds the comparison", on the contrary, it allows you to equal the lumen output of both projectors. A difference in lumen output will cloud the comparison
Of course, when you specifically want to compare the brightness levels between two projectors, you will not put a ND filter on any of them, because this will cloud the comparison. The brighter projector can light up larger screens (In order to comply with the standard brightness for projection, you need the projector to produce 12-16 lumens, per square-foot of the screen, or in other words 12-16 Foot Lamberts).
But, when you want to compare overall image quality between two projectors, you need to first calibrate both to give the same amount of lumen level (and you need to use a screen size that allow both to reach 12-16 foot lamberts), and only then you can draw conclusions about overall image quality, conclusions that are not clouded by difference in lumen output.
The AX200 is 3 times brighter than the Z5. So, if for example, the Z5 gives 14 Foot lamberts on the screen (which is great), then on the same screen, the AX200 will give (14x3=) 42 Foot Lamberts, which is crazy bright. Dark scenes with 42 foot lamberts will look washed out in comparison to the 14 foot lamberts of the Z5, even if the contrast (and dynamic iris quality) of both the Z5 and AX200 is the same.
If, on the other hand, the AX200 gives 14 Foot Lamberts on the screen, then on the same screen, the Z5 will give (14/3=) 4.6 Foot Lamberts, which is crazy dark, it will look so dim you won't be able to watch it (but will have amazing blacks though).