Blackmagic video capture devices support up to 16 channels of audio. Most all other capture cards only support stereo. When hooked up to a AVR, the mac can easily support 5.1, 6.1, 7.1 as well as Dolby Atomos 5.2.1 from the Blackmagic device. If you need 4k/60 support, the Black Magic Quad HDMI (around 400 - it supports up to 4 HDMI inputs) can handle it without an issue, although you'll need an PCIe enclosure that supports an x8 connection. For 1080p/60 support, a thunderbolt based black magic device can also do the trick (around 120.00)
To display the image on the Mac from the capture cards, I use OBS Studio.