I did this last month with OEM Bi-xenons from the H7 equivalent,
its relatively easy in all honesty and you don't need to "rewire" the loom at all.
all cores you need are actually already there going to the FRM. you will need to add about a foot of ground wire for both left and right headlights to pick up the xenon ballast supplies.
i can put together a complete install build thread if you need?
this wiring diagram may also help you out.
dont forget about the coding sides of this retro fit, and the fact you will need both the self levelling units and upgraded FRM module