I have the Moondrop Quarks and the Etymotic ER2XR, so I guess I can give you some idea about the differences (and a specific similarity) between both of them. Also both being dynamic driver IEMs, the comparison is quite interesting indeed. Without further ado:
Build: ER2XR>>Quarks.
This one oes to ER2XR, hands down. Detachable cable, metal shell, unlike the cheap plastic one on Quarks. Quarks does look more expensive than the price would make you believe but it feels cheap.
Comfort: Quarks>>ER2XR
This one will vary by individual. I abhor Etymotic's deep-fit (also known as unwanted intrusion) and the ER2XR makes my ears hurt. Quarks is like a late afternoon sun in comparison.
Isolation: ER2XR > Quarks.
Overall sound: ER2XR > Quarks
Finally, the important stuff. ER2XR is indeed a wholesale upgrade over the Quarks. Let's break it down. (I won't be posting graphs here as those are available all around for both models and don't really tell about many of the actual differences)
Source: Sony NW-A55, tips: Final E-type (Quarks), Ety triple flange (ER2XR)
The most noticeable difference between these two: sub-bass. Quarks have meek sub-bass that's devoid of texture and rumble. ER2XR provides both but doesn't get near "bass-head" levels due to the rather anemic mid-bass. Mid-bass is a contentious topic and I am not a fan of the abrupt rise from 200Hz/even lower to the sub-bass frequencies since it makes the transition from sub-bass to mid-bass very abrupt. Given the relatively flat sub-to-mid bass transition on the Quarks, I actually prefer the tuning here than on the ER2XR.
However, the driver on the Quarks just can't move a lot of air and as a result the entire bass region sounds dull and somewhat hollow compared to ER2XR. Mids are similar in tone and both have a
dry tonality to my ears, but the ER2XR is definitely more resolving of the two. I didn't find either of these too shouty but the ER2XR is a safer bet if you are sensitive in the upper-mid region. Finally, the treble is no contest, ER2XR wins hands down. It's not an airy treble response but the somewhat splashy treble of the Quarks is nowhere to be found here. Timbre in general is better on the ER2XR as well, and it's far more resolving esp in terms of layering and instrument separation.
As for the rest: neither have good staging and both are below average. Imaging is also just left/right on both (and I like to call ER2XR's imaging as "negative imaging" since everything is pushed to the sides and flattened out like on a piece of paper). Quarks is not much easier to drive which is kinda surprising for a budget device.
In conclusion, I'd upgrade to the ER2XR if the deep fit isn't a deal-breaker. It's overall a superior IEM once you get used to the strange sub-bass response (or you can just get the ER2SE though that one can get shouty).
