Have you actually checked the ohms on the Vivi Nova with the ohm reader on your ZMax, or just going on what it is "supposed to be"? Individual clearomizers and cartomizers can be pretty far off from what they are supposed to be and what they actually are when you test them.
Now that I've gotten that out of the way; as Bill above said it will be a process of elimination whether your disappointing results are from the Vivi Nova or you ZMax. Try a different juice attachment on the ZMax. Try a different flavor, a different ohm, at different voltages.
I read nothing in your post that indicated that you were doing anything wrong. I assume you are aware that the top wicked clearomizers like the Vivi Nova need to be tipped sideways or the juice swirled to keep the wicks nice and wet while you vape, otherwise you can get a burnt taste.