I know you already have the info you needed but just to say that I am currently using an NX4 DSD on my desk at work and I have been using it also as a DAC only into a DSP (BSS) feeding some Meyer speakers with great results. Although my headphones aren't really power hungry (80 Ohm), I never have volume over 60% on low gain, so it is quite powerful for its size.
I have an Atom and a P20 on their way for my desk and will be using the NX4 as the DAC for them until I decide on what desktop version I will replace it with. The NX4 will then be used for portable and travel setups, doing a mighty fine job of it also
I had already ordered the D10 and was considering the D30 when I saw a review from a member here on YouTube talking about how great the D30 was, but that the NX4 from a DAC perspective was equal or even better compared to the D30 which is supposed the be very similar to the D10 concerning sound qualities. I’m not after a DAC for it to raise the highs and bass of my way-too-mid-heavy HE4xx’s in their non-amped state (shoot, they could sound way different once powered properly - though I doubt it - better once amped yes, but not a total different sound signature). But from research it seems that no one says that DACs have a HUGE effect on signature. The HE-4xx is simply not the right headphone for me signature wise. But I know the Loki will fix that because even a bit of tweak with a software EQ and a huge drop on 500K makes me like the HE-4xx a lot, they’re just distorted due to the power need created by EQing.
So I’m not after a DAC for what EQing (Loki) can do. And I’m not after absolute transparency, 99% transparent is good enough. But a EQ can’t add depth or soundstage. I’m hoping a DAC can and the NX4 is supposed to be able to do that.
I used to have a pretty powerful high end Onkyo system (I forget which model - it was 15 years ago). But there was a song that has a part where there is THX effect where the sound builds and builds in a similar sense to THX. When I would play that on my Onkyo, it had such depth and clarity that it would give me chills every time. I have been chasing a headphone solution to get me back there on that song ever since. My Audio Technica D40x’s are fine sound signature wise as-is and EQing only hurts it. But on that song it’s totally lifeless. My HE-4xx’s are much closer to my goal on that song but that is only after EQing, but it is un-amped so it distorts. I’m hoping that with big power from the Atom, better than iPhone DACing with the NX4 and EQing with the Loki, I will be to where I was with the Onkyo, or close at least.
What confuses me is that everyone calls the D40x “neutral” and everyone calls the HE-4xx fairly “neutral”. But to my ears, the D40 sounds great signature wise, and I like V shape. But the HE-4xx sounds extremely inverted U shaped (well at 500K anyway). So even if my ears can determine V vs inverted U, my ears can definitely tell that they are not both “neutral” because they are wildly different. Problems with subjectivity I suppose.