Thanks for your answer! Ok, I did a bit more research, and I stumbled upon the Ifi IEMatch. Even though it costs 6 times as much, it seems like it actually works better than the 10$ ones from DUNU. Already ordered it, and hopefully it works as expected.

I bought a new phone, the Xiaomi mi a1, and it has a built-in amp with 10V. I also have the Sennheiser IE80, with an impedance of 16 Ohm. The problem is that whenever I use those two with each other, a very annoying hizzing/static noise is to hear. The same with other headphones with low...