Hi, M. Hope you all are having a better day today. Btw curry does the same thing to me

!
Along the lines of what you,
@Jill & Alex (GA) have been thinking (absorption etc) and bc the usuals (pumpkin, SEB etc) have been of little to no help for Ty:
1. The addition of a LGI (low glycemic index) complex carb or its water such as brown rice or oat bran or oatmeal could be worth a try. Even in the liver shake recipe on fdmb, rice water (and the fundamentals of how to make it, just substitute the white rice water with other kind of rice or oatbran/oatmeal) is suggested to help mitigate diarrhea.
Here’s the recipe/info link FYI to have on hand:
http://www.felinediabetes.com/FDMB/threads/the-liver-shake-for-sick-cats.30432/
Making a liver shake might also be a way to see if Ty resonates with raw and or if the restorative aspects of the liver shake helps.
2. Nutrient absorption: another possibility that might be worth looking into in the quest for more normal poo and in conjunction with other nutrients, changing food choices: Animal biome poo pills. It’s not inexpensive, whether the gut restoration pills alone or the kitty kit (includes the gut restoration capsules and fecal testing). But I have found that since Azalea has been on them, her stool has gradually improved and her nutrient absorption, I think has improved, my indicators being that she eats more satisfyingly, her chronic fur pulling and recurring bouts of gingivostomatitis (that vets were at a loss to help mitigate and traditional options were either contraindicated or too dangerous with her age and multiple conditions) have lessened and her fur is growing back.
https://www.animalbiome.com/collections/microbiome?page=1&sort_by=best-selling
If you have any questions (I certainly did before deciding to try it for Azalea), Holly Ganz, one of the co-founders, is very helpful as are the rest of the UCDavis team involved in the animal biome project. Their site, (with additional info in their blog section) offers some very interesting info, too.
3. Trying / transitioning to raw or home prepared, cooked or raw: Worth a try whenever you feel you and he are ready whether you start by a pre made or home prepared. One source of home made using meat (no bones) only, if which the premix includes egg shell powder instead of bones) is EZComplete (food fur life). Idk if it is available in NZ or if there are similar products available in NZ but here’s the link to food fur life. They do mail out free samples so an email to them (Laurie Goldstein or Carolina liima, co-owners) would answer any questions.
http://www.foodfurlife.com/
They also include lots of information about gut health. If they can’t send to NZ, they might know of products more accessible in your country.
Hope you all have a peaceful and feeling better day!

Sina
ETA: you mentioned trying to find a LC canned food with brown rice in it. A possibility: add a bit of cooked rice or oat meal/oat bran with the water or just add the cooked water to the LC grain free canned food that he likes?