I don't have that unit, but taking a look at the manual it seems (I can be wrong):
If you're into stereo mode, you have to read the bottom labels.
In stereo mode you have 2 channels input, the Input #4 signal will come out on the high and low XLRs that are next to it.
The Output #1 and #2 comes from the XLR input between #3 and #5.
Another way to look at it is that each channel has 3 sets of XLR connections, one input and two outputs.
So, or I'm wrong or you have it all wrong.
You need 2 balanced XLR cables. One going to input 1 (between label #3 and #5) and the other to input 2 (label=4). If your soundcard does not have balanced outputs, just use two unbalaced cables.
To get the high outputs working you will need 2 XLR to RCA cables (like the sub cable. One will connect XLR high output 1 (label 1) to RCA on the receiver; the other will connect XLR high output 2 (on the right of sub out) to RCA on the receiver.
Hope this works. As I said, I don't have this unit.