The headphone: Cardased Sennheiser HD650. The player: Oppo BDP-83 via the dedicated stereo outputs using AudioQuest Sidewinder RCA cables. This is basically a mid-fi set-up, the Lehmann Black Cube Linear USB being the most expensive component.      I mostly listened to SACDs, but have played CDs, BDs, and DVD-Audio. Using the amp’s USB connection, I played MP3 files to test out the DAC.      I’ve had the Black Cube Linear for more than two months. Have managed to put in about seventy listening hours and about double that in break-in time.     ...