How to implement 5.1 audio over HDMI on a graphics card?

Question

HDMI

Hello!
The problem is this: The
PC is connected to the receiver "LG-BDHT" via hdmi on the video card "nvidia gforce gtx770".
TV is connected to the receiver via hdmi out to tv and optical fiber.
Previously, everything worked according to this scheme and pleased with 5.1 sound, but now ... In the digital audio settings of the nvidia control panel, only the stereo channel is available, there are no more options to choose from :((
When playing, there is sound in the entire system 5.1, but, as I understand it , this is pseudo 5.1 from the stereo channel (PCM2 / 0.0)
The PC has 2 sound cards installed (onboard realtek HD and Xonar DG audio), of which only xonar is used to output sound to headphones, in other cases I listened through the 5.1 receiver.
As an option, I see a solution to the problem in buying optical fiber (PC> xonar> optical fiber> receiver) But, this is not the best option, because you need at least 10 meters of cable + laying on the plinth bypassing furniture + before everything worked via hdmi, but now I can’t decide this problem. All drivers (mother, video, audio - fresh + K-Lite codec pack 64bit)
HELP, please.