sparkofinsanity
100+ Head-Fier
I used to have the M2U/M stack too. Could you go into more detail how the marantz is better? specifically about what is the magnitude of difference. How is the synergy with EL8? I can imagine it would be perfect because the marantz is neutral.
The biggest difference is, honestly, the luxury things on the Marantz (the remote, the setup functions, the build quality/design). When it comes to the sound it is harder to define, both amps have enough power to handle my headphones with ease (I don't own any hard driven cans, but there's lots and lots of headroom for the EL-8, around 11 o'clock with low gain on the HD-DAC1), but from comparing (using the EL-8's and P7's) the Marantz sounds fuller with better definition in the midrange and larger soundstage. But the differences are small and both are very neutral in sound.
The EL-8's work great with the Marantz, but I suspect this amp works great with just about any headphone (not an amp to use if you're trying to "fix" a headphone that is lacking bass for example).
I've had the EL-8's for a couple of months now, and that notch that Tyll's measurements show at 7kHz doesn't come through when I listen to them, my ears and EQ testing suggests Audezes own measurements are closer to the truth. YMMV.