I originally had the full 9005 kit to install in my stock projectors(factory halogen). I then swapped to EVOX-R projectors, D2S bulbs and ballasts, I used the harness from the original kit. I did not need any splitters for high beams. My stock halogen high beam wires plugged directly into the evox-r projectors. I do not know if this if different with factory HID.
If anything i would recommend OEM branded bulbs and ballasts. I find the morimoto bulbs take a while to "burn in" and my morimoto ballasts did not always start in the cold weather. I have not seen any issues since summer hit though, so it could be the weather or the fact the bulbs have more hours on them. Either way i suggest you go with the more expensive Denso ballasts, i plan to get these if my problems come back this fall.