Since it's a B6 it's almost certainly a Symphony II and not a Symphony I.It's the Audi Symphony.
That's a different issue to what Greeny233 was thinking - where on the Series I radios, as used in the B5, every time you moved the volume control the new setting was written to the EEPROM which as it only has a limited number of writes eventually died.Mine is the same, i have to do what mike and scott do.