Last thing to say about multichannel digital out. HDMI vs SPDIF, well people say digital is digital it won't be different, well that's not quite true unfortunately.
HDMI uses a data island period to send audio along with video, where even the video timings can 'get in the way'.
SPDIF is far more direct, the transmission is not broken up, shared by video-other.
Here is a merger of the two, where I remove the obsolete copper method, and switch to lossless direct digital. Its bi-directional, either end, either direction.
Given the range of optical, the bandwidth fall-off that you currently see with HDMI-DP will be an almost non-existent issue.
The video lane could start at 100 Gbps (NRZ-PAM2), and later move to 200Gbps (other encoding, example PAM4).
The audio and data lane can-will also have their
own bandwidth, 125Mbps audio 10Gbps data (NRZ).
Currently both HDMI-DP and SPDIF are limited in bandwidth based on HDA (HD Audio, 2004), single stream, which is ~37 mbps.
Also note that optical fiber is an insulator, it does not conduct electricity, therefore EMI-RFI are non-issues.
Note that a device can be audio only, network-internet only, video only, or combination, with return.
====
Also not only does Windows not allow you to configure more than 7.1, for PCM (compressed formats don't count), its also legacy with SPDIF formats.