Hello
When you switch on your Head Unit (Radio)
It will flash up "B O S E " before any radio or CD comes on.
I have bought a complete Bose AMP & 10 speakers for my saloon
I have it installed & it sounds great, but the head unit does not flash BOSE because i need to take it to Audi to re-gram the computer.
This will confuse the Audi guys there, as they wouldnt have a clue what to do!!!
(Sorry, being faceious)
Cant help you with the broken grill on the sub.
Get the part number & buy the new part from Audi.
Take it to a Boy Racer Car Hi Fi shop & they will fit it for a fraction of Audi...
The standard system has a sub as well as the Bose system.
Hope this helps
Cheers
David