I have spliter but my PC recognize that Sony PJ *04 projector is connected to PC so it's only give 2.0 support. I don't know can i and how to force Windows 10 to send 5.1 sound because of it.

If you want to take full advantage of your PC’s audio potential, you should connect your rig to your A/V receiver and passive speakers—or a really good set of powered speakers.