Mute HDMI?

[PuzzledGreatly]

We are currently using an msi combined Windows 7 64 bit computer with screen to watch TV as our TV is waiting repair. We7ve connected our satellite TV tuner to the computer via HDMI. This means we can't see the computer screen when the TV is showing. Is there a way to use AHK to mute the sound via a keyboard shortcut? I investigated using SoundSet and I could mute the PC sound but not the TV sound. The only thing I've found that works is using the physical volume buttons that are built into the side of the computer. They raise/lower the sound but don't mute it. Is there a better solution? Thanks.