Hi,
I as well am having the Windows 8.1 Netflix app issue. Playing Dexter season four, episode one (as an example) the frame rate is about one fps whenever Dolby DIgital Plus 5.1 audio is used. No sound is heard. Switching to stereo avoids the frame rate problem. DxDiag attached. My setup is a custom built htpc based on an Asus P8H77-I motherboard with an i5-3570K CPU. No discrete graphics are installed. Audio and video is passed by hdmi to my Denon AVR-2809.
Regards,
Mads
PS. No issues encountered pre Windows 8.1.