Bear in mind that the connector on the back of the head unit is not merely an AUX input. It is an AUX
interface. The head unit buttons can control an external device (just as they do for XM). Even a simple AUX input needs to deal with this set-up. There are relatively inexpensive solutions. The
Car2Aux adapter for Hondas is $55 & provides one set of RCA connectors.
These adapters (not just the Car2Aux shown above) plug into the back of the head unit with a:
& if used along with an OEM ((XM)) receiver, a Y-cable is needed, too.
The same outfit makes interfaces that allow head unit button control for iPod, Axim or Palm handhelds (or Treo phones), or even computers via USB. These "controller" interfaces cost about $75. They aren't as "pretty" as USA Spec adapters, but they're a lot cheaper. I've had mine for almost a year with no problems other than the 3M sticky mount coming lose a couple of times
I don't know of any AUX interfaces that will control a non-OEM ((XM)) or Sirius radio from the head unit & certainly none that display significant data on the head unit LCD. (My Car2PC adapter will show time elapsed on mp3s playing on my laptop but won't show the id3 tags...)