Despite being published 12 days ago, Ω missed this excellent writeup. Overall, Headfonia agrees with Ω: DUET is a fabulous amp for IEMs. Our opinions divaricate on the point of DUET's performance with headphones. This is Headfonia's take:

“So in case you are wondering: overall the Duet is not the same sounding as the recently released resolving, spacious and dynamic Theorem. Yes the Duet is quiet and doesn’t have any minor issues and if you want a very clear sound and bass and mid range focus and can live with the smaller sound, the Duet is for you. For IEMs the choice is easy, the strong points of the Duet make your IEM extra good as most of the better monitors aren’t necessarily tuned with a focus on bass. For full size headphones the Duet can be a great match if your headphone can use a bit of bass and mid range focus.”

The Theorem 720 has a sound signature that more closely resembles the ALO Rx MKIII-B+. For any number of earphones/headphones, that is a good thing. It is muscular and detailed. But so is the DUET. In fact, the DUET sports a lower noise floor and slightly better stereo image when driving high-current loads. That makes it a better amp for both your Audeze headphones and your low-Ω IEMs.

Ω's review is coming soon. While it will ooze sincerity, it will be almost complete ohmage. This is Cypher Labs' first nearly flawless product. 720 may have amazed me with its resolution and stand-up stereo image, but DUET sacrifices very little in delivering better across-the-board performance in addition to better management of circuit noise.

Effusive though the above paragraph may be, I believe it is important to point out that performance-wise, DUET has no Cypher Labs equal. Sound reviews are, by nature, subjective. Actual performance isn't.