Oh great.. It will be really helpful if it can encode all audio from my pc into dolby.. And i hope it has its seperate equalizer..I see you have mentioned you got Sapphire R390 graphic card on your PC, this has AMD TrueAudio Technology which mean the HDMI out on R390 should be carrying audio information along with video out. Can be easily tested by connecting video terminal with speaker i.e. LCD/LED.
Now if you decide to buy OREI HDA-925, you could connect R390 HDMI out ---> OREI HDMI in ---> OREI HDMI (ARC) --> Computer Monitor & HDMI (audio out) / Optical ---> Polk soundbar. So in this setup i don't see the need for Denon 1513.