Surround sound with an audio interface?

 I’m first and foremost a musician, then landscaper, and then somewhere down the list, a gamer.
 

For my gaming, I want to get some quadrophonic surround sound by adding in a set of old stereos speakers my parents have had for years. I’d ONLY be  using them for gaming/entertainment purposes. All eight of the outputs on my interface show up as discreet outputs; I’ve got sound working perfectly and have even set up Cakewalk to route to their output just to see how they sounded with my mixes, and have had them playing simultaneously along with my primary monitors, so clearly mixing quadrophonically wouldn’t be an issue.
 
However I can’t seem to find any settings in Windows that will let me stream 2 sets of stereo audio to 2 sources at the same time, nor to maybe 'force' Windows to treat the 2 stereo outputs as a quad-surround setup. 
 Is there some sort of “virtual sound router” or some kinda of tool, program, or driver I can download to attempt to set up surround sound in Windows 10?
If push comes to shove, I’ll just use an app that can mirror a stereo output to another output. But first I want to try quadrophonic!