Really, really stinky cat poo - help!

[Flaxbee]

This is a multi-part question/post. First, what is the best cat food diet - I know probably all dry or all moist isn't good, but is there a preferable ratio of 40/60 or 25/75? I have an older male cat (at least 11 y.o.) who is missing his top two canines so I feed him more moist than not, though I know the canines aren't used for much more than tearing meat, something he's never had to do. Then I have a 7 y.o. very lightweight female who has always done a great job maintaining her weight, I don't worry about her too much.

And then finally, the new, stinky poo guy. He's young, probably between 1.5 - 2 years and we just caught, fixed, and adopted him about 3 months ago. Vet said he checks out fine with worms, etc., and he's steadily put on weight. He strongly prefers moist food, though I haven't run the gamut with dry foods. I know many here recommend Royal Canin and Organix, both of which I'm going to try soon -- but what's the best ratio of moist to dry?

And why would the new guy's poo be SO SMELLY? He also farts a LOT (odd for a cat; I've been owned by more than 15 in my life and this guy is the first regular farter), and his poo is not really well formed, much looser than 'normal' turds, if I can say that without sounding totally obsessed with my cats' bowel movements. It also has an awful, kind of sour after smell. He's indoor/outdoor - sleeps outdoor on the screened porch and comes and goes thru a kitty door; he only brought me one mouse the first week he became a regular member of the household, and no other critters. I don't think he has a diet of much wild meat anymore because he powers through a lot of food each day and has gained probably 7 lbs since we brought him in - he's big, about 20 lbs, without an ounce of fat on him; when we first caught him he had an upper respiratory infection and even though he weighed 12 lbs, he was bony.

Thanks for any insight...