Male cat urine is THE WORST! Had the same experience many years ago... new brand of litter wasn't a hit.
I used vinegar, allll kinds of cleaners... I went as far as to pour Pinesol on the carpet!
"They" say if the odor isn't completely removed, a cat will revisit the same area... and ours did. All carpet was completely removed shortly after.
Let us know if you find something (safe) that works.