Regarding crystals, I just found this link. An interesting read to the how's and why's.
http://www.petcaretips.net/why_bladder_stones_form.html
Wysong Uretic is specially formulated for cats who are prone to urolithiasis (stones forming in the bladder), which is why I mentioned it.
Those Eagle Pack digestive powders are great too, but I'm not sure if they'd change the PH balance of the urine and help with crystals... do they? Anyone know?