I am running an IPOD Nano through the aux port on the HK radio on a 2007 Ultra.. The volume is not that great..
I tried to increase the volume by running it through a small Boosteroo amplifier. As soon as I do, this it kicks off all volume on the radio. This configuration works well elsewhere.
I run a Gen3 Nano 8gb and I pretty much max out the volume on my Nano. You might also check on your Nano under your "Settings"and under "Volume Limit" make sure your volume can max'd out.
My ipod nano plays at just a little more than half the volume the radio plays. Didn't figure it was worth it so I decided to burn CDs in the mp3 format instead. I got almost 100 songs on my first CD with room to spare.