Actually, 10.7 should work... Just did a bit more research on it. Basically, we had been building wxWidgets with QTKit, but in Sierra, they completely removed QTKit so I cannot build it anymore. Thus, I flipped it over to AVFoundation which was introduced in 10.7. (QTKit was marked deprecated in 10.9)
Anyway, it SHOULD work... Could you run:
otool -L /Applications/xLights.app/Contents/MacOS/xLights
and
otool -L /Applications/xLights.app/Contents/Frameworks/libwx_osx_cocoau_media-3.1.1.0.0.dylib
and check to make sure all the required libs are found and within the right version ranges?