DTS bitstreamed as AC3

I have a HDMI tv box connected to a LG TV, which has an optical out connected to a DD5.1 system. Of course, no problems occur with DD / AC3 streams, but DTS streams are played in stereo, despite I set 5.1 channels out. Windows audio settings can only be set as stereo, so I tried and set AC3 encoding in ffdshow (disabling LAV for DTS), but it eventually works only on S/PDIF because it still sounds like stereo. How can I bitstream my decoded audio in AC3 through HDMI?

Edit: now it works, with AC3 encoding... just updated audio drivers and Win10...

You can probably enable DTS again now that the driver works properly.