Most of the USB code floating around is based on the HID class. However, if you download the current Microchip Libraries for Applications (MLA), and go to:

mla/v2018_11_26/apps/device/audio_midi

there are examples for numerous PIC devices. Of course, it will be written in C, and will have to be opened in MPLABX. That's about as much help as I can offer.