Maximum number of audio channels over HDMI Is MacOS Mojave capable of sending more than 8 audio channels over HDMI?

For example, if I purchase a DisplayPort -> HDMI 2.0 adapter, will I be able to select more than 8 audio channels in the MIDI settings app?
No.
It's not a Mojave limitation, per se - DisplayPort can only carry 8 channels, up to 192kHz 24-bit, max bitrate 36,864 kbit/s 

Source Wikipedia - DisplayPort