Hello all, new QDC owner here. Unlike others, i do not experience "white noise" with my LG G6. It's the quad dac version, H870DS. However i do agree that the neptune can't handle high dynamic range at high volume. It simply distorts quite a bit. Although...whoever listens at that volume is probably deaf anyway.
After 2 weeks of owning the neptune...i can say that its tuning is easy on the ears. It's definitely not flat though. Build quality is excellent and I absolutely love the carrying box. The neptune was powered via a LG G6 or the AK320. Sound signature on both sources are similar, with the AK320 providing better resolution. Ran single-ended with PWaudio copper28 cable (I hate the stock cable as the mic kept poking me and it felt rubbery and tangly).
The bass has a lot of body but not too much depth. There isn't much sub-bass. I find the bass to be more than enough for most tracks, with good control and impact. Sometimes there's too much midbass, especially on Daft Punk's RAM. But that's just me; someone who even finds the andromeda as a little too bassy. The mids are sweet and slightly forward. Vocals are clear but slightly warm, but I like it a lot. Reminds me of the Earsonics SM3 mids. The treble is the part that disappoints me sadly. Perhaps it's just that most of my IEMs have excellent treble; ER4S, Andromeda, Kaiser Encore and some others. The treble of the neptune is just enough. It's very average i guess. Don't get me wrong, it doesn't sound bad. It's just that it doesn't have sparkle or good extension. A little EQing will improve the treble slightly, but don't expect a huge change without introducing distortion. Oh yeah, sounstage is pretty average too; not wide nor too intimate.
What QDC can do to improve the neptune; introduce a driver to handle the treble. Tune it so that it doesn't sound peaky, but provide good air and sparkle. With the other driver to handle the mids and bass, perhaps it could be tuned to reach further down to have some sub-bass rumble that's needed for some tracks. Oh, and perhaps more colour options, though I'm loving the blue tone of it.