Are you using a USB-DAC or a passive USB-C to headphone-jack adapter? If it is a passive adapter, I guess the Fairphone 6 has a worse DAC or your connector could be bad. Otherwise I couldn’t tell what the cause could be.
I tried 2 DAC’s and a passive adapter and for me with a passive one it is also kinda meh in terms of quality and volume.
The two DACs I referred to are both active: The hifi has a high end DAC by Audio Note. It’s one of those settings where you just want the sound to shine. And it did with my old FP3+, just not entirely the same with FP6. Which I find just strange. And the smallest movement of my phone makes it disconnect from the DAC and pause the music, which I’m not used to either.
The mobile DAC is a Fiio, and actually I can’t make it work with the FP6. I suspect it has to do with the micro-usb→usb-c adapter I’ve been using. I just find it strange that FP6 can’t find the DAC as an audio unit when FP3+ does it.
This last issue actually made me buy a passive Fiio DAC, in order to listen through headphones, and this DAC plays without issues for me. Luckily!
You mention “The mobile DAC is a Fiio, and actually I can’t make it work with the FP6”, but then later say “made me buy a passive Fiio DAC… and this DAC plays without issues for me.” - so I take it you have 2 Fiio DACs, one works with the FP6 and the other doesn’t? Which model does work? About to receive a FP6, and want to get a DAC for wired IEMs, but don’t know which will work. Thank you!
I would give that a chance: Maybe it could be necessary to install a new FW via another smartphone if provided by FiiO. I’m not sure it’s only a cable-related thing. I guess the overall chain of FiiO DAC/Cable/FP HW/Android Audio Stack (…) can be slightly fragile.