Blocked Urethra Recovery/Diet

My 4 year old Harry is home from 3 days at the vet hospital with a catheter.  I decided to reject the Royal Cannin/Hill's Prescription diets because I've heard too many horror stories.  Harry's diet previously was a grain free dry + 1 serving of FreshPet Moist Refrigerated.  His first day home I only gave him very wet canned food and now he has diarrhea.  Does anybody know how I can transition him to an all wet food diet?  I guess I'll have to give him some dry (and maybe some rice) for awhile to firm him up but I'm just nervous about giving him dry food now.  Any thoughts/suggestions/experiences please. Thanks!

This article might help:
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You'll find that many members here have used the prescription "urinary" diets made by Royal Canin or Hills successfully. Our last cat was on both brands for several years following a bout with struvite crystals (which he interestingly enough developed after a grain-free dry food was added to his diet).

Hopefully some members will be along soon with suggestions for you.

Thanks.  Yeah it's not that he doesn't like the wet food -- he loves it. It's the diarrhea.