I downloaded the 4.3 update and I couldn't regret it more. If you use your phone in a car dock, it is now utterly useless. Car home Ultra won't start when docked anymore. And the home button no longer works. Just takes you to the non rotated home screen and you have to select an icon to get back. Extremely unsafe. I downloaded a couple other car dock programs and they have the same problems.
Also had my car wired specifically so I could use a USB to audio in. Phone calls never went to the car stereo because of Samsung programming limitations. But it was fine because I could be connected to bluetooth and voice calls automatically switched to there. Not now. USB audio only works when NOT connected to bluetooth. So if I want to listen to audio files and a call comes in, I have to turn on bluetooth quick enough to catch it. Again very unsafe. I work from my car quite frequently and now I can't even take calls. The car dock functionality is about what I had ten years ago. Might have to finally give up Android.
Re: Thinking about updating to 4.3, read this first.
Try SoundAbout from the Play Store. It lets you reroute the different audio streams wherever you like. You'll have to buy the pro version for $2.99 though, 'cause the free version doesn't let you control Bluetooth streams.