The UDP needs to be set to Source Direct to pass through the video to the capture card.
Instead of this UDP you can utilitze any 5.1 pre-amplifier which supports an audio codec currently used by Netflix, Disney+, Amazon Prime, HBO Go, etc. If you use a pre-amplifier with variable output volume make sure you adjust the volume so you don't need to post-process amplification to it.
While Netflix has a desktop client from which you could separately record 5.1 audio, other streaming clients on Windows do not have this feature.
Video: Mi Box S → 40281 (HDMI) → Intensity Pro (HDMI)
Audio: Mi Box S → 40281 (SPDIF) → AVR-4308 (5.1 through Pre Out) to U86XT (Line IN 1-6)
Make sure you connect the U86XT through a Ground Loop Isolator to the AVR to avoid ground loop issues while recording
Set the AVR-4308 to volume -10 dB
VHS Stereo (Intensity Pro)
Video: HR-S6711EU (composite) → Intensity Pro (Y - green)
Audio: HR-S6711EU (stereo) → Intensity Pro (RCA)
Audio monitor: HR-S6711EU (stereo) → AVR-4308
OBS Studio
Settings
Output Hint: Chose Simple or Advanced, not both, then save. Simple is good for lossless recording of both video and audio. Advanced is only necessary for some special use cases.
Output Mode: Simple
Recording Path
Recording Quality: Lossless Quality
Output Mode: Advanced
Type: Custom Output (FFmpeg)
File path or URL
Container Format: matroska
Audio Bitrate: 256 Kbps
Audio Track: 1
Audio Encoder: pcm_s16le
Audio
Sample Rate: 48 kHz
Channels: 5.1 or Stereo
Video
Base (Canvas) Resolution: 1920×1080
Output (Scaled) Resolution: 1920×1080
Downscale Filter: [no downscaling required]
Common FPS Values: 60
Properties Intensity Pro 4K
Video Connection: HDMI
Audio Connection: Analog RCA (we do not record the audio stream)