Xenon bulbs light output fades as the bulbs ages so that could be part of the problem. It might also be worth checking that they are not set too low from the factory. They can be adjusted with an Allan key on the headlight themselves.
My neighbour’s 11 year old Audi has new Xenon bulbs in. They are nice and white and have a good light output. If I was in your situation I would look for quality bulbs from a well known brand.
Just had a look and Philips do a D3S White vision bulb which may be of interest to you.
