It appears that in the US we call it a Euro adapter but in the UK its called a BMW adapter. At least after looking at the site Scott posted, it sure looks like the BMW adapter is what you want.

Good luck and please post the results of your JVC install. I'm most interested in whether you use the existing speaker wires and harness or if you convert your speaker wires into RCA leads and use your pre-amp outputs as discussed in your other post here.