Sorry, but Quad is QUAD - you need 4 inputs to get 4 outputs! If you only supply a stereo sound then that is all you will get back out. Some sound systems can create Pseudo-surround sound from stereo, but not this one.
You would need to somehow feed the same signal to the rear amplifiers, but there is no control to do this.
I can't even get the Record level control sliders to show - The software is rubbish compared to the sound quality, which is very good!