convert 3 x 3.5mm stereo jack plugs to a toslink optical cables?

I’ve just got a new sound card for my computer and the only way it will output true 5.1 surround sound is through the 3 x 3.5mm stereo jack plugs directly to a set of surround sound speakers how chessy. It has a set of optical toslink cables sockets on the rear but you have to disable the 5.1 setting and run only 2 channel stereo to get them to work and i’ve been told that the reason for this is to protect copyrights ? Why? All i want to do is connect my PC to a surround sound amplifier so that i can play pc games that i brought in true surround sound, i’ve no intention of copying anything but i just want better quality audio