I've got good news for you, and bad news for you...the good news is it may not be cat pee, the bad news is it may be 'cockroaches' (or some other bug)...and not necessarily the bug.
We ended up with a system from a bar room once, fired it up, and low and behold the lovely fragrance of 'ode de puddy tat'. There were several dead cockroaches inside, but they were not the actual culprit...turned out it was the 'poop of the cockroach'. This required many gallons of 'distilled water' and a toothbrush to clean.
Remove everything that can produce heat, from power supplies to audio cards, soak in a solution made from 2 gallons distilled water, with 4 capfuls of "Simply Green" cleaner [any other 'environmentally correct' one will work just peachy].
Rub it down with a toothbrush, rinse with fresh distilled water, air dry, reinstall.
Should work. Don't do things like motors (if the problem persists...I would recommend sending the motors to a 'motor rebuilding shop'), have a fire extinguisher handy when you restart the machine in case you ^#$%ed something up (disclaimer on my end in case something goes wrong).
You're going to find the low end response a little squirelly on the 7800...other than that, neat machine.