The dongle will detect your Amp's input impedance, which is typically very, very high, >600Ω to a few kΩ I think. That way, both versions should unlock their full Vrms. However, there's a good chance that they will clip if you put them to 100%, so be aware of that!
the 9038D will probably have the same noise floor as the S G3. I start to notice it with the 107dB/mw, 17 Ohm Se215. Most of my other IEMs are silent. You could probably mitigate that with the ifi IEMatch, but there are some reports about sonic changes, so it's not a perfect solution.
The OTG Y-splitter is necessary if you want to use the 9038S with an external power bank to preserve your phone's battery life for example.
OTG was only necessary for the G1. The newer devices have no need for OTG.
For use with a PC I recommend a basic USB A to USB C cable from Anker or Aukey...
No it's not fine. Your DAC and Amp have to share the same ground. The otherwise resulting ground potential could seriously damage the DAC. the thing is that the 9038S doesn't have a ground contact like a normal, balanced DAC has (3rd pin of a 3pin XLR jack), so to get ground from the 9038S, you...
The 9038S cannot be used with external Amps or active monitors unless you know what you're doing and how to DIY your own cables.
Only the 9038D is able to be used as a standalone DAC.
Neither the 9038D nor the S have EQ. That is a feature exclusive to the PDv2, which also cannot be used with...
It is digital hardware volume.
The volume is saved after unplugging.
Both the S8 and the HD Pro use a TRS 3.5mm jack from what I know. That means that neither support a mic or inline remote.
I have yet to experience EMI with the S8, though I haven't used it extensively.
The 9038S G3 is now available on AliExpress!
I will refrain from listing all the improvements so as to not sound like a salesman, but if you're interested, then you can read more on the website or on the Discord server.