All digital devices will use some amount of memory. Audio devices are all digital these days and only use a DAC (Digital to Analog Converter) to generate the actual audio waveform from a raw sample stream.

On something like a standalone audio amp there still has to be the whole backend to store codec information, menus and settings, and a whole host of other controls and audio processing features that are likely implemented on top of a basic OS and not directly written to a microcontroller. There's more memory than you think.

Depends on if you have analog cabled headphones, like the Meze Empyrians or the Philips X2HR Fidelio, then they are analog, but wireless or even digital headphones with USB/Lightning has ram.

This is probably all like stand-alone Bluetooth speakers and such that have little processors in them. Analog hifi shit isn't going be able to use AI for anything except maybe receivers or something. I guess there might be a use case for using it to balance to a room and set up EQ or something, but these guys don't seem interested in doing anything that would require actual work to develop a real product.