eXistenZ_Born: I have however since discovered a nice workaround to the issue, which is working for me. I'm running Win XP 32bit OS and by going to volume controls and changing the 'SW Synth' volume bar this raisers and lowers the in-game music but not the voice. I load up the game completely then Alt-tab out and change this setting as the music is still playing for me Alt-tabbed, if you don't want to do that, setting the SW Synth bar at about 2 or 3 is a good setting.
This fix is possible on Windows 8/8.1/10, but it requires a few more steps.
[ I've only tested on Windows 10 64-bit, but it should work on Windows 8 and possibly 7 if Microsoft handled MIDI the same way]
Problem: The 'SW Synth' has been locked down in Windows, preventing you from modifying the volume.
Solution: Download an application that has a MIDI mixer.
I use:
http://coolsoft.altervista.org/en/virtualmidisynth If that link is dead (I think they have bandwidth issues), Google 'Coolsoft Virtual MIDI synth'
After installing it, download a sound font, such as:
http://www.synthfont.com/SoundFonts/FluidR3_GM.sfArk Extract it with:
http://www.synthfont.com/sfArk.zip Now configure CoolSoft (Open the application called "Configure VirtualMIDISynth"):
* Press the '+' button on the right side, navigate to and select your soundfont ('FluidR3_GM.SF2' if using the example above)
* On the 'MIDI Mapper' tab, set the Windows MediaPlayer Device to CoolSoft
* On the 'Options' tab, check the box to "Automatically open the MIDI Mixer while playing"
* Hit "Apply" and "OK" buttons on bottom
When you open "The 11th Hour", a mixer should pop up. Move the master slider all the way to the bottom, and then up a tiny bit (to 3% or4%). Some non-MIDI sound effects (like the wind/rain at the beginning of the game near the front door) are still loud, but the soundtrack is softer and most dialog is understandable.
I hope this helps!