Squalks, I'm sure there was some recent chat about this, or at least to someone wanting to change to the 06 bi xenons. IIRC figures around the £2k were mentioned.
No idea what they're talking about with 6 prongs or 4, but (and I really am guessing here) but maybe they're trying to work out whether you've got the 06 model or earlier. I would imagine that they'll be a plug for the lights to connect into and I would have thought if its a bi xenon there may well be more prongs on the connector??????
Sorry can't be more help.