dont get the 6000k! well.. my two cents personal opinion would tell you that they are too blue.. they dont match the other HID kits that come OEM in higher end vehicles these days. i think the ones that most vehicles come with are the step lower than 6000k. i hear 6000k is OEM for the A4 though, this may or may not be true. they look borderline ricey blue. also, think about this- closer you are to the higher end of the color spectrum, the less stress you will have in your eyes especially prevalent in long term driving. blue is at the low end while red and purple are at the high end, right before ultraviolet.
ever look into a red light in the middle of the night? does not affect your night vision. ever wonder why lighting in tactical aircraft as well as your audi use red lighting? same reason.
the VVME kit is great. just make sure not to mount them in your engine bay as you MIGHT experience outages due to the 105F overheat trip sensor in the kits. that area below your headlights that looks like something mounts there? yeah thats where the OEM ballasts go.
as long as you have the facelift housings with the projector lights you should be straight. although i read the OEM HID housings use beam focusing rather than the halogen OEM projector housings which just use a peice of metal that cuts off the light. the focusing in the lens is probably the reason most OEM HIDs have that nice clean cutoff at the top of the headlight beam.

 

acutally those halogens are going to burn out your battery a helluva lot faster than the HIDs.
HID bulbs do not use a filament, the metal spiraled thing in the bulb you see in halogens.
they actually use a xenon gas discharge and run at 35 watts in continuous operation. your halogens run at 70 watts although, they require a 24000 volt spark to ignite the xenon salts contained within the bulb. dont be startled by this because thats probably about the same size capacitors one or two of your point and shoot camera's flash uses.
HID's are bright as all hell man, we use the same gas and technology in one of the infrared seeking missile countermeasures systems on my aircraft, it uses a super bright concentrated beam of light to blind a shoulder fired missile, basic stuff. except it ignites it into some sort've plasma instead of a gas...

 

OEM HID kits are all 4300k. The 6000k are not even remotely ricey blue - they're a bluish tinge to look at and that's it. The light on the road is very, very white (and much less fatiguing than halogen light). Go up to 8000k and the lights appear very blue on the front of the car - the road lighting is bluish but not horrendous. Luminosity is cut down a decent amount though.

As for the VVME kit tripping on an overheat, I haven't seen that happen yet, despite several people I know having the kits mounted in the engine bays of many cars (including cars that run much hotter in the bay than the A4). Below the headlight is a great mounting spot though, but not necessary to keep the ballasts from tripping. The OEM ballasts mount into the back of the headlight housings.

HID housings are ideal for use with aftermarket HID kits, but you're perfectly fine using housings that were originally made for use with halogens - you still get the sharp cutoff and have no temperature issues with the lenses.

 

I pulled some stock fogs off a 1.8 in a junkyard and paid 15 a piece for them