Long time Bengal with litterbox problems

Ok everyone, I am sure you have heard it all before, but I will be as specific as possible. I have a Bengal, one cat out of 5. They all get along pretty well, but the Bengal has issues with the litterbox. He tends to pee outside of it, and in different locations. I have puppy pads on all the places where he pees, and changed out the floors to hardwood to deal with the issue. He is 11 years old and in good health. or so I think. We have been using "worlds best" cat litter for years, and in his area, switched to "cat attract" which has been helping, but it's a terrible clay litter. But it seems to work somewhat. But he still pees outside the box on the pads. He has been to the vet many times, many x-rays and nothing. The food he eats is royal canin 32 and 38. He loves wet food, and drinks mostly bottled water. He drinks water all the time, so he is not dehydrated, but his pee is very pungent. He is not very active, but when he has pain pills, he does get active. When he does pee on the pads or away from the litter box, and he does understand that he is doing wrong, and hides under the bed after I catch him. He knows he is wrong, but still does it. What am I missing here?

Thanks in advance

Mike

I would take him to the vets to start with, hopefully with a pee sample.  You don't say what he eats but if mostly wet you shouldn't see him drinking much.  The FAB has a useful page about 'inappropriate toiletting' and some of it comes down to 'cats are cussed':

http://www.fabcats.org/behaviour/spraying/info.html