USB Device Classes
Is there any way to support being a different USB device class? Like USB Audio class to allow SPRESENSE to be used as a sound processor?
It should be possible.
You would need to implement the USB device class driver in NuttX.
See this documentation: https://nuttx.apache.org/docs/latest/components/drivers/special/usbdev.html
As examples they mention drivers/usbdev/pl2303.c and drivers/usbdev/usbmsc.c.
You could create a driver called drivers/usbdev/audio.c for instance.