I do understand your concerns and I would not settle on something hissing, in particular at the iFi price point. If posting to iFi is not a practical option, I would honestly return it to the dealer, get my money back and go with something else.
Again, thanks for the advice. If the vendor is willing, I'll do as you suggested.
Just some updates, as it seems none of the ifi products without iematch builtin is a good match for me. My ears are just too sensitive it seems... Now that I know what I'm looking for, I tried the different models available in the store, namely the xCAN, Nano BL, and Micro BL.
To ensure it is not just my own, I used the store's own demo unit of QDC Neptunes (10 ohm) which is much lower impedance over the DMG so it's quite noticeable. The xCAN and xDSD both exhibit hissing for me. The Nano would exhibit hissing in direct from 0 volume up to maximum. For reference, the store personnel there could only hear the hissing in the Nano from around 50% volume and up, and anything lower is inaudible for them and this is using the QDC Neptune. The Micro hissed but only with iematch off and on turbo/standard. On Eco, even without the builtin iematch, it did not hiss at all.
Aside from the Nano, the others are tested first with audible music for me then I cut off the music to try and see if the hiss is audible or not.
They also had a Chord Mojo demo unit, and I tested it out as well. There was a weird sound, reminiscent of dial up internet while connected to my phone (wifi and lte was on) which I assume was RFI. Aside from there being RFI on the Chord Mojo, it also had a slight hiss, but much less noticeable compared to the xDSD. For the Mojo, I had to concentrate on trying to hear it, which, while not ideal, is simply so much better compared to the xDSD imo where I could hear it easily as long as the environment was quiet.
All the hissing disappears when used with Ifi Earbuddy or Iematch btw, so that's my last resort if the store does not allow me to exchange it for another item. There was another item at the same price range that did not hiss at all for me, even when I put it on High Gain, but I'll probably just post in that thread if I do get that item. Sad, because without the hiss, I actually preferred the sound of the xDSD over all the others, even over the Chord Mojo(this sounded super smooth and velvety though so taste might depend on day).
PS, the Neptune is at 10 ohm, and I mistook the impedance rating for the DMGs as it is apparently 18 ohm, not 28 ohm which is what is listed in Penon Audio. Maybe it's the BA drivers that I can hear causing the hiss, as the hiss was even less noticeable on the F300, which is at 16 ohm and a single dynamic driver.