The transducers are the most important components of any audio chain. For recorded playback of digital signals, there are three: the DAC changes the signal from digital to analog; the speaker (or headphone) changes the signal from electrical to mechanical; the brain interprets the signal from mechanical to neural impulses and perception. I argue it's the last one, the brain, which has the largest impact.
The brain and the DAC are certainly part of the chain, but they're not transducers.
The definition of a transducer is device that converts energy from one from to another, such as electro-acoustic (speakers, microphones, vinyl cartridges), electro-mechanical (potentiometers), etc.
DACs and amps operate solidly in the electrical domain so are not transducers.