It's in the registry. On my system I tested to find where it was by changing just the main volume and this is what I found had changed.
Info gathered using InCtrl5:
QUOTE
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\DeviceClasses\{6994AD04-93EF-11D0-A3CC-00A0C9223196}\##?#PCI#VEN_1102&DEV_0004&SUBSYS_10031102&REV_04#4&1C660DD6&0&10F0#{6994ad04-93ef-11d0-a3cc-00a0c9223196}\#WavePci\Device Parameters\Mixer\0\Controls\0 "Channel0"
Old type: REG_DWORD
New type: REG_DWORD
Old data: 08, D7, 00, 00
New data: 00, 00, 00, 00
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\DeviceClasses\{6994AD04-93EF-11D0-A3CC-00A0C9223196}\##?#PCI#VEN_1102&DEV_0004&SUBSYS_10031102&REV_04#4&1C660DD6&0&10F0#{6994ad04-93ef-11d0-a3cc-00a0c9223196}\#WavePci\Device Parameters\Mixer\0\Controls\0 "Channel1"
Old type: REG_DWORD
New type: REG_DWORD
Old data: 08, D7, 00, 00
New data: 00, 00, 00, 00
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\DeviceClasses\{6994AD04-93EF-11D0-A3CC-00A0C9223196}\##?#PCI#VEN_1102&DEV_0004&SUBSYS_10031102&REV_04#4&1C660DD6&0&10F0#{6994ad04-93ef-11d0-a3cc-00a0c9223196}\#WavePci\Device Parameters\Mixer\0\Controls\0 "Channel0"
Old type: REG_DWORD
New type: REG_DWORD
Old data: 08, D7, 00, 00
New data: 00, 00, 00, 00
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\DeviceClasses\{6994AD04-93EF-11D0-A3CC-00A0C9223196}\##?#PCI#VEN_1102&DEV_0004&SUBSYS_10031102&REV_04#4&1C660DD6&0&10F0#{6994ad04-93ef-11d0-a3cc-00a0c9223196}\#WavePci\Device Parameters\Mixer\0\Controls\0 "Channel1"
Old type: REG_DWORD
New type: REG_DWORD
Old data: 08, D7, 00, 00
New data: 00, 00, 00, 00