Can anyone answer a few questions concerning de-emphasis filters

From the MKll manual
“Some Compact Discs were recorded with pre-emphasis in order to improve performance at high frequencies. If you are playing a track that was recorded with pre-emphasis, you can manually engage the de-emphasis filter using the option. Set to On to engage the de-emphasis filter. Set Off to disable it. The default is Off”.
I turned this filter on yesterday and, generally, I enjoyed the effect. But I have questions. I also found an Auto setting in the menu. I would assume this means there is a way the DAC can detect this pre-emphasis. Possibly some kind of tag imbedded in the digital signal. If so, is this technology only used with Red Book CDs? Is this feature useful with streamed CD material? Was pre-emphasis abandoned with the advent of hi-res? Shouldn’t all DACs offer a de-emphasis Auto filter as the default as CDs, or any digital format, really doesn’t require a feature to “improve performance at high frequencies”. Does pre-emphasis explain why so may CDs, especially early ones, sound so bright and “digital”?