I am not too happy about light output of PF headlights myself, especially on full beam and considered changing to FL. From what I could see you need to change bumper, wings and bonnet for everything to line up.
At the end I just used LED bulbs which have improved light output a lot and passes MOT without any issues. I used these on S8 for both dipped and full beam
http://www.aliexpress.com/item/2x-Pl...280472297.html They are a bit big on the back and covers does not fit back on. I just used black duct tape to seal it up so that dirt and moisture does not get in light and put a bag of silicagel inside to absorb the moisture and prevent condensation. They do have a temperature control and will switch to 60% light output if they heat up too much. Never happened on S8 but on the A6 they fit behind the covers and will dim after couple of miles as the airflow is not good and they don't cool well. I have also used these
http://www.aliexpress.com/item/High-...522553813.html and these
http://www.aliexpress.com/item/2015-...305907244.html in A6. The last ones seem to give out the most of light and have integrated fan to cool them but not sure how long the fan will last being moving part but I don't think they will fit under covers on 8. The other ones should fit OK. There are a lot of different designs available but you cannot really tell which ones are better until you try and compare them.
I have also disassembled and cleaned light reflectors and lenses which helped a bit but reflectors were not in a good shape with the shiny coating coming off in places so I am considering re-coating them.