I've gotten a little farther along.  Here's what I discovered so far:   - USB stick needs to be formatted FAT.  exFAT (which is the default used by Windows in some cases) doesn't work.  You will need to download a utility that will force a FAT format.  Just search for 'HP USB Disk Storage...

Just picked up my Model S today and was unable to get it to work with the AK120 either through USB (in either DAC or USB drive mode) or pairing with Bluetooth.  My phone paired no problem but could not get the AK120 to pair.  The AK120 recognized the car but the car did not recognize the device...