Do anyone know definitively if the original blue Alpine 6.5"-ish premium door speakers used in the X400's were 2 ohm, 4 ohm, or 8 ohm? I've been digging through old posts here & elsewhere and while 8 seems unlikely, I have seen all 3 answers. In my specific case it's a 2005 X-Type Sportwagon with premium sound and nav, if that matters.

 

without garantee... so far I know...they are 2 Ohms

 

I have just spend some time trying to find that answer on the net...
I even found pictures of the Jaguar sticker with the part number (2W9318808BC) that way, i.e. even if I were to remove the door-trim and the speaker to look at that sticker, I would not find any more information. This sticker on any other speaker gives you the impedance - but apparently not on Jaguar speakers....

Thus, I can only give you an option based upon me being a High-Fi / High-End enthusiast as well:
I would definitely avoid 2 Ohm. Any normal head-unit will blow a 2 Ohm speaker into smithereens.
Normal Impedances are 4 Ohm and 8 Ohm, and I think Bose also uses 5 Ohm or 6 Ohm.
My personal preference are 4 Ohm.
If you use 4 Ohm speakers on the system designed for 4 Ohm , you are obviously spot on,
if you use 4 Ohm on a 8 Ohm system, you have to restrain yourself from turning up the volume too much,
if you use 8 Ohm on a 4 Ohm system, you will not be able to properly "turn up the volume"...

 

perhaps you may find the answer here:
here:

 

Yeah, this thread & related ones lean 4 or 2 ohm for the doors but never decide for sure (at least that I saw). With some additional confusion about the fact that the front speakers are the same part as the rear speakers but effectively get more power because they get their own unshared channel from the amp vs splitting it with the tweeter in the rear doors.