HD600 – MacBook Pro internals: Look I’ll be honest. I expected the sound of the HD600 to sound bad, veiled and congested, lacking in the low end since the amp in the MacBook is nowhere powerful enough. If you’ve ever seen the data from innerfidelity, you can see the spike in the low end, almost 550 ohms at 100Hz! There’s just no way the 2VRMS output jack of the Mac can deliver enough current. Still the HD600 is such a great headphone, it still sounds awesome unamped directly from the minijack. It’s just less detailed/precise compared to with the Schiit stack. After a while you start to notice little faults though, little details sounding too harsh, more complex parts of music start to blur.
HD600 – Modi2u & Vali2: With this setup the HD600 truly starts to shine. Details come alive. The quality of the bass is better, more defined. The quality of the midrange and highs is improved as well, although less significant. Soundstage is good. Separation is improved as well, although it still gets a bit blurry when the music becomes to complex, just way less to a point that it becomes nitpicking in my opinion.
When I use low impedance and high efficient headphones I switch to low gain on the Vali2. The difference becomes less apparent, since the output jack of the MacBook is more than capable of driving the lower impedance/higher efficiency headphones. For example my SR60e are 32 Ohm/99.8 dB SPL/mW. It comes to a point that I would advise you really don’t need a separate DAC/amp for these kind of headphones.