Garry's Mod COMPLETELY freezes when changing speaker setup

[VikeeVeekie]

Today I have adopted my father's old 5.1 home cinema set (JVC RX-E100R), as it doesn't have default 5.1 PC audio connectors I'm using a 3.5mm-RCA cable, I have enabled Speaker Fill in Enhancements, and after that I launched Garry's Mod, went to change the speaker setup, the game totally freezes as soon as I apply the change, this even occurs when I disable Speaker Fill.

Any ideas? I ran out of options here :C

Update - L4D2 changes the speaker setup without any hassle.