Multiple audio devices USB

Hello. I'm continuing to work with USB, I need to evolve from USB Micro+Speaker to multiple microphones. I failed at descriptor.
Whole descriptor here

The structure of USB+Micro is next:

• Device descriptor
• Device qualifier descriptor
• Configuration descriptor
• Interface association descriptor
• • Interface descriptor #0 Control
• • • Header
• • • Clock descriptor
• • • AC Input terminal [Speaker]
• • • Feature Unit [Speaker]
• • • AC Output terminal [Speaker]
• • • AC Input terminal [Micro]
• • • AC Output terminal [Micro]
• • Interface descriptor #1 Speaker
• • Interface descriptor #2 Micro

I tried two descriptors both failed for me. I don't know if it is my mistake or concept is wrong.
In the first attempt, I did the same things I did when I added micro to speaker: two more terminals and one more interface:

• Device descriptor
• Device qualifier descriptor
• Configuration descriptor
• Interface association descriptor
• • Interface descriptor #0 Control
• • • Header
• • • Clock descriptor
• • • AC Input terminal [Speaker]
• • • Feature Unit [Speaker]
• • • AC Output terminal [Speaker]
• • • AC Input terminal [Micro]
• • • AC Output terminal [Micro]
• - - AC Input terminal [Micro 2]
• - - AC Output terminal [Micro 2]
• • Interface descriptor #1 Speaker
• • Interface descriptor #2 Micro
• - Interface descriptor #3 Micro 2

Then I found another thread with a similar question. Guy there added one more IAD with interfaces

• Device descriptor
• Device qualifier descriptor
• Configuration descriptor
• Interface association descriptor
• • Interface descriptor #0 Control
• • • Header
• • • Clock descriptor
• • • AC Input terminal [Speaker]
• • • Feature Unit [Speaker]
• • • AC Output terminal [Speaker]
• • • AC Input terminal [Micro]
• • • AC Output terminal [Micro]
• • Interface descriptor #1 Speaker
• • Interface descriptor #2 Micro
• Interface association descriptor
• - Interface descriptor #3 Control
• - - Header
• - - Clock descriptor
• - - AC Input terminal [Micro]
• - - AC Output terminal [Micro]
• - Interface descriptor #4 Micro 2

My problem is I don't know what's wrong: a mistake in descriptors (size calculations, id numbers, etc.) or the concept itself.