Ignore handsfree calling with bluetooth enabled car stereo?

I installed an aftermarket car stereo so that I can stream audio from my iPhone. Unfortunately the stereo also intercepts every phone call that I get and tries to make them hands free. The quality is horrible on phone calls and siri can't understand anything when it is connected.

All I want to do is stream music. Any ideas on how to get the phone to ignore the stereo mic and handsfree?

This was bad until iOS 7 and much worse in iSO 8. Previously I just had to tell the phone to use the handset 1 time per car trip. Now every single call connects to hands free. This is distracting and dangerous...