hi sorry for kitties problems its so hard when they are ill and we are sometimes at such a loss to what to do...I would recommend getting him into a Vet right away, if he's crying around the litter box its a very good indication of pain, any crystals can cause a blockage at anytime. Diet will make a big difference with the struvite crystals(I have one of mine with this too) you have to be very sure you are feeding canned food NEVER DRY with crystals/or CRF kitties.
I'm afraid if its oxolate than diet doesn't work, only surgery that I know of will be of any help. canned food does help pass more urine though b/c of the higher water content.
Please post again if we can help at all and update us on Max please....good luck♥
I was dealing with crf and the best information I found was on a website Tanyas, CRF something like that. if you google it Tanyas' CRF Cat it should come up. Educate yourself now, because when a cat starts going down hill again it is quick and you need to have knowledge and a game plan. Find a vet that understands CRF and crashing. Dehydration is a prime concern. But I'm not sure where it fits with crystals I do know that a cat not urinating is a medical emergency. I used homeopathy with my cat for different reasons will good results before CRF, but CRF is serious, it's a constant balancing act. Don't rely too heavily on alternative supplements that could actually hurt. NO alcohol, really none., good luck and spend all the time you can with him. I just reread your post, Sabers' blood levels looked good too, so the vet obviously missed something and I,m left trying to figure out what it was.
http://www.felinecrf.org/symptoms.htm
I agree this is a great site for anyone dealing with CRF....best luck to you and kitty♥