Happy Birthday Slashdot, from a long time mostly-lurker.

There are quite a few aftermarket head units that provide aux input of one sort or another. Observe:

Blaupunkt Montreal CD34

Kenwood KDC-MP6025

Sony CDX-F5700

Clarion ProAudio DXZ545MP

Panasonic MXE CQ-C5410U"

Rear auxilary inputs are far from being a new feature or found only in high end in dash recievers.