Did you run a culture on the urine? I think I mentioned elsewhere how culturing has become my go-to for pee test now—the regular kind is just too insensitive to rule out bacteria (I think they miss over 30% of infections, which has been about right for MP, too).
Did the vet say why the urine isn't concentrating as much despite no obvious increase in water intake?
I'm glad that the CBC/Chem came back normal! That's a relief.
Hope you can get it under control, soon!