[peva]

as far as I know it is only on models with the Infinity system

You are correct - center dash speaker comes with Infinity I and Infinity II systems only.

Keep in mind if you think you want to add that speaker that the factory amp that comes with the Infinity systems has a separate output driver for that speaker, so you'll have to figure out how to drive it (possibly the one wire from the rigth front channel and one wire from the left front channel - one neg. the other pos. - just a guess - but that should work).