Congratulations!!
Are you using the RME as your headphone amplifier as well?
In other words, are you happy with the all-in-one function, or are you planning on adding a separate head amp to the RME?
I'm using it as a headphone amplifier, yes, with a pair of Beyerdynamic DT770 250Ohm, mainly. Without EQ, it can drive them louder than I can bear listening to - and I like to listen loud!
When I add EQ and bass boost however, I can sense the limits of the amp, but only when I want to listen really loud. And when I mean really loud here, I'm talking just shy of club PA system levels of bass. It can definitely make the cans vibrate on your ears!
I listen to mainly electronic music and hip-hop so I'm very picky about bass and it has indeed satisfied me. When I crank it all the way, I can hear the drivers in my DT770s distort from what I think is them hitting the plastic shielding in front of them. This is all with about -2dB of headroom left on the ADI-2, so if it indeed isn't clipping, an amp wouldn't be of any use if the headphones themselves can't handle more volume. However I'm not sure as to whether this is because I'm reaching the limits of the amp or my cans.
On my other pairs of lower-impedance headphones (Grado SR125, Sennheiser HD25, Sennheiser HD280, Sony XB700, Slate VSX), there is PLENTY of power - I haven't even gone above -15dB with the bass boost activated for fear of ruining their drivers.
But for 200+Ohm headphones, if you're a basshead and like to listen loud, an amp probably wouldn't hurt. 200Ohm seems to be the ceiling for the amp in this, I would not be satisfied if i had 600Ohm headphones without an external amp. But in the end, you're buying this for the absolutely brilliant DAC and DSP - if you or your cans are power hungry, it only just scratches that itch.
I was actually shopping for an amp but ended buying this instead, and despite not having all the output power in the world at my disposal, both the EQ and DAC more than make up for it. My Beyers sound like they cost three times as much. Even my non-discerning girlfriend thought the difference between the ADI-2 and my old DAC was night and day, so you know the DAC in this thing is absolutely bonkers. It's a cliche, but I have found myself yet again rediscovering my music library.
Also related to all this – I'm very impressed with the metering on the unit, as it displays the output volume post-fader so you get a reading of the actual headroom left in the amp after all DSP operations and even the volume knob.
I'm going to bring the DT770s and ADI-2 along with me to a hi-fi shop tomorrow and see what (if any) improvements an amp might bring. Will report back.
But TL;DR: if you're listening on 250Ohm cans and don't want hearing loss, it's more than adequate. If you loooooove loud music (bring on the hate brigade), consider pairing it with an amp later on, and you're honestly set for life.
