Hi
I would only use ZF lifeguard 6, because its never a good idea mixing oils.
would only buy genuine ZF aswell, aftermarket filters allways seem to leak.
Genuine kit comes with oil, filter, new pins with larger heads and new mecha sleeve, which were prone to leaking on the electric connector.
when you change the oil, only about 6 litres drains out of the box, about 4 to 5 litres stays in the torque converter.
never known any body have any issues with using zf lifeguard 6, but a lot of people who use a different brand seem to get problems
also, when changing the oil, ideally you should clear the gearbox adaptations, so the gearbox learns how to shift again and you get smoother shift, sometimes putting fresh, slightly thicker oil in, can make the gear changes quite harsh, also reseting the adaptations can only be done with software like Jaguar ids/sdd and some icarsofts, disconnecting the battery does nothing. Adaptation reset is allways done if the service is done at jaguar.
also if your getting harsh shifts, if the gearbox has never been updated, software update can cure this, last update was 2009, my car was a 2004 and had its original 2004 software, updating mine cured the surging/hunting when it was cold at around 30 to 40 mph.
cheers
Joe