There's probably not something specifically for what you want to do, but you could probably hack something. I'm assuming you're trying to stream music from your phone directly to your amps? You might be able to use a bluetooth stereo headset and plug the headhone out to your amp in. Maybe something like the Jabra BT3030?
Edit: Actually I have a Jabra BT3030 and there may be one problem with it. It does not work while charging. It does last for about 4-5 hours on a single charge, depending on usage. If you were to dedicate it for this usage, you'd probably want to setup a relay to provide a constant charge while the car is off, then cuts it off when the car is on. That way you'll always have a fully charged Jabra.