I recently spent a few weeks exhaustively reviewing five headphone DAC-amps. They included the Schiit Fulla ($79), AudioQuest DragonFly v1.2 ($149), Oppo HA-2 ($299), Celsus Companion One ($595), and Sony PHA-3 ($1,000). Of course anyone who buys one of these products will find that the listening experience depends heavily on the headphones used with it, and there's no predicting which headphones an individual buyer may use, so I chose a varied selection: the Oppo PM-2 ($699), Sennheiser HD600 ($400), and Sony MDR-V6 ($110). Then I had to choose the demo music. That was fun—anyone who says a job like mine isn't fun should find another job—but it took some care and forethought. Just as associated gear affects perception of an audio product, so too does the music.