Apologies if this has been asked before, it's a bit difficult to search for "PCM" and "USB" when both PCM and USB are too short to be valid search terms

I've got an '09 Cayman S on the way with PCM nav and aux audio input, but I wanted to know a bit more about what to expect from it before it arrives. I spent about an hour at the dealership today, fiddling with the PCM on a 997.2.
iPod/iPhone hookup and playback works perfectly, but I was hoping I could use a USB hard drive for significantly more storage capacity. I've got a 500gb usb drive from Seagate, but the PCM didn't seem to recognize that it was plugged in. The drive lit up, meaning it was getting power over USB, so I'm not sure what the issue was.

Do any of you guys out there with PCM in a 997.2 have experience with this? What do you use for audio storage?

Thanks much,
/c