Having used several brands of coilovers on my old mk4 golf I feel I should say that spax coilovers had a real bad reputation for reliability. Didn't have them myself , I'm a kw fan, but my garage who deal with a lot of modified cars say they're terribly unreliable and offer very poor aftersales care for parts etc.
Not saying the A8 ones will be bad but just thought I'd let you know..... Especially as the A8 spax coilovers are a lot more expensive than the old golf ones........