I'm guessing here, but ...

There's 1 port in the back of your headunit. That 1 port can be used for an add-on-item such as xm radio, navigation, a cd changer, or the mp3 player.

When looking at this installation manual, http://handaccessories.com/accord/04audio.pdf , I see there is a " Y " shaped splitter cable. If you have XM and navigation, both split signals are occupied. If you wanted to remove the XM, you'll have one spot open for the MP3 player.

The MP3 player has a list price of $403.20 and plays MP3 cds. That's it. For that price, I'd rather get an iPod with this.

the Belkin Tunebase


it broadcasts the iPod over an FM signal, so no additional wires are needed. The sound isn't as clear as a CD, but this might be your best option for MP3 playback.