I thought it was worth resurrecting this thread to address whether IOS6 makes any difference. I have exactly the same problem with the dock output persistently switching to bluetooth, as has been outlined extensively in this thread. A2DP Blocker works, but is a bit of pain, so I decided to take the advice of other posters and apply the car software patch. I contacted the local Volvo dealer (yes, I am one of those wretched Volvo-owning thread-hijackers đ ), who insisted that he was 99% sure that IOS6 would solve the problem. I tried it, and unfortunately he was wrong. It made absolutely no difference. It is a shame that Apple have missed the opportunity of a major upgrade to sort this out, e.g. by giving an option to switch off A2DP. They will now be so busy fixing the widely advertised problems with IOS6 to bother with this for now. I will now do battle with the Volvo dealer to try to get them to install the car software upgrade, the details of which the other posters have kindly provided.
Incidentally, I am a bit cross at having been bounced into making this OS "upgrade". I had heard about the Apple maps fiasco, but thought that if the bluetooth problem was not solved, I could simply revert to IOS5. WRONG! It is not possible to "downgrade". Also, I suspected the alleged map problems were exaggerated (these things often are), but alas they are not. It is not just the occasional town that has in incorrect or missing name; it is a substantial proportion of them (~30% locally). Moreover, the aerial views used to be excellent high definition views where you can resolve houses, cars etc., but on Apple maps must have been taken from a satellite orbiting Mars, with a greasy lens. However, I digress.... I just wanted to warn anyone that IOS6 is NOT the answer to this problem, and to think very carefully before making this so called "upgrade", since it is irreversible. Does anyone want to trade an iPhone 4S with IOS5 for one with IOS6....?