kou iu VS konna

Hi, I would like to ask about the difference between the words above. I understand that konna can be used as "konna ni" (and kou iu cannot), but I am not sure how to differentiate them in terms of describing someone/something. Any help is deeply appreciated. Thanks.

I will just give some examples -

(1) Before you start telling someone a story/anecdote you've heard from someone else, you start off saying:
- XXX-san kara konna hanashi wo kikimashita.
- XXX-san kara kou iu hanashi wo kikimashita. (I heard such a/the following story from XXX-san.)
[So either can be used before a noun, saying "this kind of..."]

You are trying to show someone how to cook something - how to cut some veggies.
- Konna fuu ni kitte kudasai.
- Kouiu fuu ni kitte kudasai. (Please cut in this way/manner.)

(2) You show someone a photo of your dog - it was just a small puppy a few months ago! and you say:
- Konna ni ookiku narimashita! ((The puppy) grew this big!)

You are trying solve a math exercise, and it's the most difficult one you've encountered:
- Konna ni muzukashii mondai wa hajimete da. (It's the first time I bump into some exercise that is this difficult.)
(With "konna NI," it is more like an adverb that comes on top of an adjective. Colloquially, you can say "konna" in the above sentences as well.)
[[Here you cannot use "kou iu."]

In what kind of sentences have you encountered those? :)

(3) You show up at a friend's acquaintance, through introduction of your friend. The person you went to see does not know you. You present your name card, and say:
- Watashi ha kou iu mono desu. A-san no tomodachi desu. (This is who I am. I am a friend of A-san.)
[Here you cannot use "konna." This "kou iu" is more used literally in the sense of "I am a person called by this name/title," as if to quote your name, which is one of the usages of "...(to) iu.)]

In what kind of sentences have you encountered those? :)

Umm...I've encountered them in lots of places, and I just wonder what their difference is...So I gather that most of the times they are interchangeable? All right, thanks AK (as usual) ^^

Well, under (1) either can be used, but under (2) that's only "konna (ni)" and not the other can be used, and (3) is where you can only use "kou iu." :)