I agree with what Sherry said, but I'll just add an emphasize a few things...
1. You cannot fix the litterbox problem until you fix the runny/smelly poo problem. So that needs to be the focus. Forget about trying to find the perfect litter, or the perfect place for the box, or the right amount of cleaning and all that. When he goes, he is in great discomfort (thus the meow), and nobody is working to get that solved for him, so he's trying to find a solution on his own (i.e., seeing if "going" in different places will help). So he's not going to suddenly have perfect litterbox habits while he is in that much discomfort. Next time he goes outside the box, and you end up with the unpleasant job of cleaning it up, apologize to your cat for not helping him fix his problem, and use it as motivation for yourself to work harder to get it fixed.
2. It could legitimately be diet related. So the first thing to do is to immediately see if you can discover *exactly* what his diet was when he was at the breeders, and go back to that. Presumably he was going fine while he was there, so you need to try to replicate that success. You should though, keep in the back of your mind, that you might be also dealing with a parasite like TF here. There's articles on that here in the forum, lots of discussions and experiences with that, and lots of advice to be had. There's also a ton of material online about it.
https://www.petmd.com/cat/conditions/di ... richomomas. I would recommend resetting his diet first and seeing how he does with that. Give that a week or so, then if he's still having the same poo problems, getting a TF test done.
Now just some other less important comments (those first two are the biggies for right now, but this is stuff for further down the line...):
1. When he left the cattery (too early as Sherry pointed out) he had an opinion of what a litterbox is. What size, what shape, whether it was open or closed etc. He also had an opinion of what the litter was like: how deep it should be, how it smelled, how it felt to his paws etc. So, again, just like with the food, you want to replicate that success what he was having with all that, as much as possible, before even thinking about "transitioning" him to what you want him to use going forward. There probably isn't a bigger change that you could have made, of going from a clay or grain type of litter to a pine one. What possessed you to do such a thing? Even if he didn't have this terrible "poo problem" that he has right now, I *still* wouldn't be surprised if he had serious litterbox aversion problems, just because of this monumental and ill-advised change that you made. Also, just an opinion, but I really hate the idea of pine-based litter. It's really un-natural for them, the texture of it alone has gotta be awful to climb up a pile of that stuff, go, and then not really be able to bury his waste (which is his instinct), so I would re-think that long-term, even once he is "reset" back to using the litterbox consistantly and successfully, with his "poo problems" a distant memory.
2. Food-wise, you should never mix dry and wet food together in the same bowl (if that is what you are doing). The wet food will coat and contaminate the dry food, making it unsafe for him to eat unless he consumes it immediately. At his age, he also needs to be eating ~6 or so meals a day, so you either need to be leaving out dry food all the time, or be there to feed him those meals throughout the day. And male bengals will grow like crazy and get to be *big* cats, so eating with a good appetite is a big deal to them.
3. You're giving him awful food. I gotta say that. Depending on the specific formula, here's the first few ingredients of that garbage:
Chicken, Brewer's Rice, Corn Gluten Meal, Poultry By-Product Meal, Soy Protein Concentrate, Fish Meal, Soy Protein Isolate, Soybean Meal
So it's actually, on paper, it's an extremely high-protein formula, but he's getting a bunch of that protein through by-products (which should never be in a cat's diet) and soy (which is even worse).
There's some really good articles to check out here:
http://www.littlebigcat.com/nutrition/s ... -pet-food/http://www.littlebigcat.com/category/nutrition/