Ok, as I see things, drivers for some audio cards are ****ed up. It's turning 7.1 by auto when you're using 2 channels (aka 2 speakers or handset). So you need to change that default thing - mine is "Speakers (SB live 24-bit)" - to Digital Audio Interface (or whatever secondary option that is available). So, just under "Device" in mixer (the big window where you adjust all volumes, the first adjuster on left side that is master volume for everything) you just need to switch the default thing to something else (if available!). Can't be more specific than that
Anyway, if you only have one option, try installing the newest driver for the sound card and maybe that alone will solve the problem, or at least give you the option to do the switch I was talking about
Anyway, tell me if and how you did it Good luck!