Pioneer CD-MC20 Microphone
Crutchfield Customer Review (What's this?)
Like others have said, it's Pioneer's mic for measuring Time Alignment, etc. if you want automatic TA, you need this. I'm glad I bought it as the auto TA from my new AVH-4200 really does help to create and shape a decent sound stage. It's not perfect but it does make a BIG difference in the sound. Use auto TA, and EQ your cabin to a flat response and you will have a very decent sound stage w/o tons of fiddling.
Pros: Enables auto TA
Cons: Should come with the NEX units