The short explanation
You have two blunt options with EDID. Pass the display's own data through — accurate, but you inherit any gap in it. Or load a generic preset — predictable, but it no longer describes your actual screen.
AutoMix does both. It reads the real EDID from the connected display, then overwrites just the fields you select before passing it upstream. Everything you do not touch stays exactly as your display reported it.
Where you run into it
Most real problems are one flag wide. VRR that never gets advertised. An HDR mode you want removed because the source picks it and the display handles it badly. An audio format the receiver claims but cannot decode. AutoMix lets you fix that one thing without throwing away the display name, its timings and the rest of its capability list.
How the DR HDMI 8K handles it
On the DR HDMI 8K this is the COPY TX SINK EDID and MODIFY mode. Video flags cover FRL rate, VRR, ALLM, HDR mode and Dolby Vision; audio flags cover L-PCM, TrueHD, DD+, DD, DTS-HD MA, DTS and one-bit audio, most with their own sample rate options. The Dolby Vision data block sniffed from the display can be carried into the mix, so DV still works even with an AVR in between.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.