Bluetooth mono microphone while audio output is phone speaker, wired headset, or some other audio output

If you have the SoundAbout Pro key, then the Bluetooth functions are enabled.  

If you go into the phone's widgets, there is a widget called "Bluetooth mic toggle".  

This widget will allow using the Bluetooth device's microphone for voice searches, but leave the audio output set to what ever you have set in the app.  

The microphone will stay on while this widget is ON.

You can also try using the SoundAbout Voice Search capability in this thread:
https://soundabout.forumotion.com/t708-soundabout-voice-searches-bluetooth-hands-free