I assume that you mean your HTPC Motherboard has OUTPUTS for 7.1.
It's not a matter of wires/connectors for hooking it up... you need an amplifier, either internal to the receiver you will purchase or separate. You will not be able to use these speakers with only the line level power coming off the motherboard. (Except for the subwoofer. It has an amp so you would be able to use that with the line level output. But the sub without the speakers probably isn't what you are going after...)
Buy a receiver and this gets a lot easier.