I'm not sure why you are seeing that scanner volume icon, I have a couple of MC40s here and it is not on either of them.
Regardless, there is an API call to specify which audio stream the scanner uses for its volume (ScannerConfig.AudioStreamType - Zebra Technologies Techdocs ) and you can specify the alarm or ringer so hopefully that will work for your application
I can't seem to get it working on those 3 streams.The streams volume turn up, but the volume of the scanner beep doesn't.
But when i manually change the volume (using settings) of the stream i posted the picture of (the one with the question mark), the scanner beep volume does turn up.
Here is my device information:
OS BUILD: 02-13-10-4AJ22-K-F0-M1-031116
SERIAL NUMBER: 16204522700215
MX VERSION: OSX Version: TI_OSX_4.5-2
MXMF Version: 126.96.36.199
EMDK VERSION: version 188.8.131.52