Hi-fi systems generally require three elements. You need a source (to play the music), an amplifier (to necessarily strengthen the audio signals) and a pair of speakers (to output it). But each job ...

There are a couple of reasons I suspect it's taken this long to see a vacuum tube in a pair of headphones. Tubes are hungry ...

the ability to mix in ambient sound from the amp/DAC’s built-in microphone; and the option to engage a crossfeed function that makes the sound more like what you’d hear from speakers in a room.

You have your passive bookshelf and floorstanding speakers, but there are now wireless speakers and active speakers with amplification built in that negate the need for a separate amplifier, and many ...