My A6 has the OEM D2S bulbs set as low beams and I was looking to replace the highbeams(halogen H7's) with the D2Rs that are used in cars such as the lexus IS300. Since the D2S have projective properties, and the D2Rs have reflective properties I figured it wouldnt be that far of a stray but I was wondering if any sort of ballasts would have to be involved due to excess energy? Its another DIY project im working on and was curious to know if it could be done. Thx

 

Yes, you will need ballasts. The wiring harnesses for your low beam OEM HIDs are connected through power ballasts to drive those bulbs, but since your high beams are halogen, no such ballast is present should you want to install HID high beams. If you decide to do it, you need to order a full HID kit, not just the bulbs - get H7 style D2R bulbs (you are correct on that - it's a reflector housing so D2R is the correct bulb style). This will allow you to have full dual-beam HIDs. If I were you, since high beams are purely for maximum visibility, if I were doing this I'd order 4300k color temperature. It is the closest to natural daylight and is rated with the highest luminosity of the HID kits.