Expanding on this reply, you can think of Kernel Modules as Windows drivers. Most of the time they are meant to be used as an interface on which you can communicate from the OS with an underlying device more easily .

And usually they are paired with a user space tool for even easier interaction. Ideally the driver should expose literally every function and possible action and then the userspace tool has the job of simplifying that down and not supporting very unusual or complicated setups.

You could think of the userspace side as the gui you get with gpu drivers which interacts with a separate kernel space side

How did you end up doing USB with the Arduino? Was it bit banged as well (VUSB)? Is this code available anywhere?

The newer arduino's come with a pretty powerful IC for the usb interface. So I reflashed that using LUFA. To be clear the audio quality was awful, but could certainly hear what was playing. Here is the repo for it. I did it as a self directed class in university. Treat it like I had no idea what I was doing trying to understand lower level programming! https://github.com/ElementalWarrior/ArduinoAudio (This was in C, not part of the Arduino ecosystem with the IDE)

Interfaced with an FTDI chip maybe?