Could you be a little more specific? It's hard to figure out what's going on with your system when you provide little to no information as to why it's not working. I have 5.1 on my computer and it works just fine... here's a couple questions to get you started:

What kind of computer?
Are your drivers updated?
Is Toribash updated on Steam and you're sure it's 5.1?
Is Steam updated? (I do happen to know Steam is having connectivity issues at the moment.)