Audio driver: no stereo mix, mic won't mute

[Airlane1979]

Toshiba laptop. Windows 10 64 bit, Conexant SmartAudio HD driver. I want to record streaming audio in Audacity but I can't mute the internal microphone without muting all the audio, and there's not Stereo Mix in Volume Control. I've installed Realtek HD driver as an alternative but it fails to appear in Device Manager or Recording Devices. What is the solution?