Question - the intaller routed the USB cable that came with the unit to my glovebox. This provides a USB port into my glovebox.

To this I attached an standard Apple ipod cable and my ipod. All of my library info, playlists, album artwork, etc. is visible on the HU, but I get no audio.

Do I need the PIO/USB-50V?

yes you do, mine did the same

Its best to get this cable anyways. I was going to try and hit the cheap route and not get it, but after much consideration, I bought it. Its always better to have everything you need, then to keep taking the whole dash apart and reinstalling things. Plus this will allow video, full on-dash control of your ipod and charging.. Well worth it imo, I just think the $50 price tag is a bit nuts.