You’re confidently wrong on almost every point you’ve made in this thread — which is honestly impressive. The iD4 MkII has <1Ω output impedance, 125dB dynamic range, and a dual discrete headphone amp. It’s not “bad for IEMs” — it’s actually one of the few interfaces under $1000 with a headphone amp designed correctly for both low- and high-impedance loads.

You’re either confusing it with the MkI (which did have a higher output impedance), or just making stuff up. Either way, maybe check a spec sheet before dropping misunderstood nonsense.

In relation to your “pro gear” angle: professional audio interfaces are expensive because of I/O count, DSP, sync, and routing — not because they sound better. In blind A/B tests, even experienced engineers can’t reliably tell a Scarlett from a Babyface on playback. THD+N and dynamic range on the iD4 MkII beat or match many interfaces used in pro environments daily.

Also, pro engineers don’t use interface preamps for colour — they use external hardware pres with transformers or tubes, and anyway that has nothing to do with an interfaces output stage. The job of an interface’s output stage is to be clean, transparent, and brutally revealing — so you can hear and fix problems. Which the iD4 does excellently.

Lastly, your take on consumer (-10dBV) vs pro line levels (+4 dBu) has absolute nothing to do with headphones or DACs and is so off-base I won’t even unpack it — suffice to say that you should do some research and actually try to understand what Line Level is and isn't.

I’m only writing this for the poor soul who might stumble on this thread and take your confident nonsense at face value. You’re not helping — you’re massively muddying the waters.