What's wrong with which man is loud?
"loud" means that he is shouting, not that he has tons of muscles (= strong/fort)
but doesn't fort have several meanings
Generally, it means "strong".
It can also be an adverb, meaning "très" (very): "je suis fort en colère" (I am very angry)
Would "Qui homme est fort" work as well?
No, because "qui" is a pronoun, therefor you don't use it in front of a noun.
"quel" is an adjective that goes with nouns, and agrees with the given noun in gender and number.