Is there any app to mix audio sources? I currently use a running app with audio coaching via Bluetooth. When I'm at the Gym, they have headphone jacks on all the machines to listen to the audio from overhead TV. I'd like to be able to connect to the TV audio, and pass it through to the Bluetooth headphones while still hearing the audio cues for my running intervals. I know I'll need an adapter for the input since the mic-in is Mono only, but not finidng anything that can pass thorough and combine the audio sources. Is there anything that can do this?