[HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Control Panel\Theme "LargeScreen"=dword:00000001
Don't be too sure of that (there being no way to raise max volume)... there are values which appear to refer to decibel gains, and if so, it might be possible to push the amplifier a little harder. It's something I've been meaning to investigate; I saw the values a while ago and will need to find them again, though.
In fact, one of my upcoming projects is a registry search function...
Look at @GoodDayToDie s Native Access Libraries, you can find the original function in the sources,