To reset the windows audio mixer in Batch you can use the following snippet.
This snippet will set all volume levels equal. If you know a simpler way to reset the audio mixer, without setting all volume levels manually please let us know.

Sample Batch

@ECHO OFF
ECHO Resetting Volume Mixer Settings!
NET STOP Audiosrv
NET STOP AudioEndpointBuilder
REG DELETE "HKCU\Software\Microsoft\Internet Explorer\LowRegistry\Audio\PolicyConfig\PropertyStore" /F
REG ADD "HKCU\Software\Microsoft\Internet Explorer\LowRegistry\Audio\PolicyConfig\PropertyStore"
NET START Audiosrv