> ALSA additionally specifies every 2 channels as separate 2channel devices, so your 8 channel audio interface looks like 4.
There is no such specification. It is device-dependent and abstracted through ALSA configuration. Creative Labs indeed implemented their cards as three separate codecs, while ForteMedia used a single 6-channel codec that you can open as such at the hardware level. In both cases, you can open a single virtual "surround51" device that routes the channels correctly.
coreaudio doesn't need pulse nor jack nor pipewire to allow a single device to be opened by multiple applications.
ALSA additionally specifies every 2 channels as separate 2channel devices, so your 8 channel audio interface looks like 4.
the confusion is added to by device tree overlays such that you may find your pro audio 8 channel device is always seen as a surround setup, replete wirh highpass filtering on the principle pair of outputs, and you don't know why your poor desktop environments sound device doesn't show this...