I would say the preamp is more the spinal column. It links everything together. The DAC is really the "brain" because it is generating the decisions on analog waveform. The preamp or spinal column is just linking and transferring those messages to the amps / muscles. The hands/feet are the physical speaker medium moved by the amps/muscles. The "heart" is really A/C electricity. lol.
Is the preamp the “heart” of the system?
For many years my preamp was a passive devise. I was in love with the transparency. Then one day I to try an active one. With so many Stereophile “the best at any price” rave reviews I decided to go with the Audible Illusions M3B with the John Curl phono boards. I was thrilled! Finally I understood. They sound finally had meat on the bones and a musicality that I was missing. And it was just as transparent! I guess the preamp IS the heart.