What is your sound source? Meaning, are you just using the sounds in the module or are you running VST?
If you are just using the sounds within the module, this is easy. You just need a small mixer to run the output of both modules together.
It's a little trickier if you are running VST. Mainly because you need to have a good understanding of Midi and there is two main ways to go about it. But, basically it would look like this:
1) If the VST can recognize two different USB midi sources at the same time (this would be the easiest VST way), then you just connect up the two module and map the sounds you want. Just make sure you are using different midi note numbers on your second module so it doesn't interfere with the first module.
2) If your VST only recognizes one USB midi source, then you will have to run one module's midi out to the other module's midi in (again make sure your midi note numbers in module two are different from what you are using in module one). Then you will have to set the master module's midi out to "Thru". This way midi is being sent for both modules via the master module and the computer only sees one midi source.