Asking for help with Objective 2 headphone amp options. Would mostly be using Sennheiser 6xx and AKG 7xx Massdrop headphones. Source is a Harman Kardon HK3490 (with a built-in DAC) that I'd connect via RCA's. I live in the U.S. so assuming I'd go with the 110V standard version (1.0 x 3.3), is that correct?
I'm also assuming (perhaps wrongly) that digital content (Spotify and iTunes) would be processed by the DAC in my receiver.
Another question is whether this unit would improve the sound quality measurably. The receiver has Dolby Headphone. Per HK tech support (via another messageboard) the HK3490 has a" 270 ohm resistor in between the speaker outputs and headphone output. The power amplifier in this model is discrete circuitry and the preamp is op-amp based."