TL;DR: Use MacOS to get uncompressed 10-bit 4:2:2 quality video and 7.1 audio into Channels for $125
The 3g has broadcast capture quality. It has SDI or HDMI input, audio up to 8 channels (7.1) on HDMI or 16 channels SDI. The 3g does 10 bit uncompressed video.
It's Thunderbolt 3 powered and only the compressed video hits the disk.
I use ffmpeg and the libx264 software encoder for better quality and have no issue with simultaneous encodes. (One could sacrifice a little quality and switch to h264_videotoolbox or h265_videotoolbox hardware encoding.)
The audio comes in LPCM duplicated on two channels so it will work immediately with stereo but I determined I could add a filter_complex to re-package as 5.1 or 7.1.
ffmpeg -f decklink -channels 8 -i 'UltraStudio Recorder 3G' -filter_complex "[0:0]channelmap=FL-FL|FR-FR|LFE-FC|FC-LFE|BL-BL|BR-BR:5.1[aout]" -map 0:v -map "[aout]" -pix_fmt nv12 -c:v libx264 -profile:v high -crf 25 -c:a aac -
I use a (currently private) python script with browser interface using all async to process the stream from ffmpeg into channels using pyatv to control AppleTV.
BMD Recorder 3g will work on Mac/Win/Linux having Thunderbolt-3 (or better). Only other requirement is ffmpeg compiled with BMD Decklink support.