i would say zauji mumtaaz. seems like the mim from the second word is "glued" to the first. thats why it sounds like zauji had a mim at the end. :) edit: because zauji is a noun without an article, it has to have "un" as an ending. you only skip the "un"s at the end of the sentence, as far as i understand it.
Got a case of the over-literal translation going on. "Great" or "excellent" husband doesnt take, only "amazing" or "outstanding". It may be that ممتاز means literally "that which outstands", im not at that level yet, but if that is so then the course is following the letter rather than the spirit of the rule, not a good practice in language teaching.
The -un ending on زَوج is pronounced but not written. I think nunation (-un) pronounced can indicate indefiniteness and that the nunation would get dropped when اَل (ˀal = alif+lam, "the") is added to it at the start to make a noun definite. I'm just a learner, however, so go with what a moderator says and locate an Arabic grammar to explain it (The one I use is A. S. Tritton, Arabic, pp. 24-25 Lesson 1 "Noun and Articles"). I think both the noun and the adjective get the -un ending, however, as in "a big garden" نُسْتَان كَبِيرٌ (= my first time using an Arabic keyboard; cut-and-pasted; took me about ten minutes to figure out).