I just wanted to provide another update for those who might still be following this thread. As of this weekend, we'll officially be 3 months into the daily Vitamin E and Potassium treatments. As a result, our cat has never been better. He's now stronger, better balanced and more rambunctious than he's ever been in our time with him. He's just like a small child -- he'll play until he's utterly exhausted and then just drop and sleep wherever that may be. His litter mate (who never had a problem but who was historically more active) now cannot keep up.
I will not speculate as to whether the root cause was food related or whether the cat has an inherited disease. Regardless, we could not stabilize the cat on cat food alone and the treatment seems to have worked miracles.
It is amazing that this is the same cat. Our vet will be floored when he goes in for his routine check up.
Some posters here expressed a concern with the food that we were feeding our cats. Give our lifestyle and the fact that our two cats have very different eating patterns and appetites, dried food with wet food as "treats" is really our only option. We are in the process of switching them over to Innova's Evo line of dried cat food (currently we're blending this with the rest of our older cat food). They love the taste (way better than their previous favorite of Wellness brand) and they seem to have no negative side effects.
I cannot comment as to whether they eat less total volume when on the Evo food versus other foods. Many sites on the web have rumored this. I'm doing some testing though (days to eat a set amount of food) and I'll report back when they're 100% on Evo.