Humm, so i thought id ask something about what you can and can't do with usb on nexus 7. To start off with, i've built a simple rig on my car for this tablet, to work as multimedia interface. And it works awesome. The one thing that bugs me, is that the sound quality from the 3,5mm headphone jack going into my car stereo auxiliary input, isn't as good as the USB input on my car stereo.
This leads to the actual question, would it be even close to possible, to have a "virtual" .mp3 file or something like this, "mounted" as the usb? Like, when you plug the usb cord between car audio usb <--> nexus 7, the car audio would think the device has only one track, but that would be like a live stream of the tablets sound interface? I have absolutely no experience in anykind of coding and thus im here to ask you. I might be way out of boundaries on what can be done, you tell me!