audio inputs for '03 X5

I recently bought a 2003 X5 with premium radio and rear seat DVD (don't really care about that, just had it). It didn't come with a CD changer.
No NAV either (I already had a Garmin).
When I thought about how to improve the entertainment options I realized that more CDs wasn't something I needed as much as I needed built-in sound for my iPod, for other MP3 players and for my PDA. A local auto sound shop wants to install a device (I think it's by "Dension"?) that has a headphone-type audio input, an iPod specific audio input and a USB input all side-by-side. It all wires to the head unit in the X5. Supposedly it'll read and display data from the iPod (song title, artist, etc). They want about $300 including installation.
Is this a good way to go or are there better options to get audio access to the devices I use? If I do go with this device is there a generally accepted optimum place to install it? WC
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