How to play movies with multi-channel FLAC or other formats and output AC3/DTS to DAC through S/PDIF?

The motherboard of my PC is Gigabyte G1.Sniper H6 (rev. 1.0), which comes with a Optical S/PDIF output. I connected it to a DAC that accepts AC3/DTS input, and then output them to my 5.1 speakers.

(My PC)----------TOSLINK optical cable----------(DAC)------------6 RCA to G9 audio connector-----------(5.1 speaker)

I know S/PDIF can only output 2-channel PCM. My previous motherboard has a feature called Dolby Digital Live(DDL) that can transcode any audio to AC3 on the fly. DTS also has DTS Connect(DTSC) which does the same thing. But my current MB didn't support these features.

Is it possible to config K-Lite Codec Pack, so the player (MPC by default) can do the same thing, like DDL/DTSC did, so I can play video files with multi-channel audio formats other than AC3 and DTS?

Yes, that is possible.

1) MPC-HC options > External Filters > Add "ffdshow audio processor" and set it as preferred
2) Double-click on "ffdshow audio processor" to access its settings, and then
3) Enable "Resample" and set it to 48000 Hz
4) Enable "Mixer" and set it to 5 channels + LFE
5) On the "Output" page, enable the "AC3 (SPDIF encode mode)" checkbox
6) Also enable AC3 passthrough

Now all PCM audio will be converted to 5.1 AC3 audio.

On the Mixer page there is an option to "expand stereo to surround". Enable that if you want to mix stereo to four speakers (front and back).

Thank you very much!