Hi, I've been selling HID kits for several years, the problem you're seeing is due to the lower resistance of the bulbs in comparison to standard ones.
Essentially you've added an in-line resistor that helps the situation, however as the ECU/CANBUS on the vehicle is not 'seeing' the correct resistance it's pulsing the lights. In some vehicles it will just kill the power to the headlight on one side or on a particular beam.
There are companies out there that sell flicker cancellers, personally I've not gone the HID route yet (Ironic really) but I purchased my R56 as a Stealer Demo, I will go the route of perhaps purchasing a set of replacement headlights, all be it without washer & leveller...
Hope this helps