List of USB-supported MP3 players

I have a 2010 Prius III, and had a question about using the factory-installed USB interface. I'm trying to find out which MP3 players are supported by the USB interface, or at least which type.

I've connected 3 different MP3 players and had varying results. Two of them I can make sense of, but not the third.
1. a very basic Philips GoGear 1GB flash player
This one works as I expected, I can see the folders on the drive on the Prius interface, but the GUI is vary basic, and not very user friendly. I can deal with that.
2. Creative Zen
My understanding is that since this device only supports the USB MTP interface (not MSC), the Prius will not recognize it. Fair enough.
3. Creative Zen Mozaic
This is one is a head-scratcher. The device is a MSC device, and shows up that way when connected to a PC. But when I connect it to the Prius, it doesn't recognize it. Is there something else I need to be doing to set it up. Didn't think so, since the Prius recognizes the Philips GoGear (ironically the least fancy of all the 3 players!). But any advice will be gratefully accepted.