I dont see why you wouldnt be able to run hid's on your vehicle as long as its wired properly, i would love to get hid's for my 964 too,where did you get yours?
I have seen those kits being installed pretty much in any car,but i have never installed any or wire any of them,but i have read some threads about similar issues and normally they turn out to be just wrong wiring.
There is a guy that sells european relay harnesses and he makes them specifically for high wattage or hid applications, i am not sure if he would make some for Porsche, i have bought stuff from him for VW applications, this is the link for Euro wires, they are really good quality btw, i hope this helps.
EuroWires- headlight conversion wiring, relay harnesses, grounding kits for VW