Hello Geraldo, hello all,
sorry for spamming the list with such minuscule details. Thank you for your message! I did not hear from other people yet, so it's probably safe to assume that no one else is already working on it. Adding a section to the quirks-table does not help, the vendor-specific interfaces still don't work. Obviously they need extra initialization.
Next step: sniffing again while running Windows in the vm. The interesting stuff is going on here: https://drive.google.com/file/d/1IlkR4ey9Gwsdrrf6jfOwNUVDtGcl_93- (Full log: https://drive.google.com/file/d/1VmSGVk8V1saw7qdPfbOH2d4HmZTrlzxj)
From this I see several URB control messages going back and forth, for example the host sending 80bbf0, and the device responding accordingly. A bit later, and after sending 44ac00 six times (hola!?!?) I get isodesc[0-7] cross-device link for input; and once more for output, and the device reports success. These appear to be my eight channels. So far, so good for a first basic overview of the structure, but the tricky part is figuring out what message is doing what. Only the manufacturer knows it, I need experiment and guessing with a lot of time and luck. Is there a common agreement where in the source code such control messages should be put? Probably an extra file?
Best, Roman