I'm having the same problem with my Presonus Studio 192 Mobile. What I have deduced at least on my rig is that the "Sets" of speakers are not setup to be anything other than "Studio Pairs" (Main out L&R, Output 1/2, Output 3/4). You can NOT separate them. My DAW as well as UC show the correct channel mapping, but nothing switches.
From a sonic standpoint, I am hearing Left out of the left. Right out of the right. Center plays out of Left and Center. LEF plays out of Right, Left Surround plays out of Left Front and Right surround out of Right Front. I even have pics showing the correct path is being played, but it's not routed correctly in the interface. UC Needs to have a firmware update supporting Surround if they do it's not easy to figure it out and i have spent at least 10 hours on this topic alone. Hope you get a better answer than I have given you, and good luck.