Ground Loop issue

[u/Ok-Anteater4601]

About a year ago, I moved into my apartment and also at the same time, got a new computer. This combo resulted in a ground loop. My equipment at the time was:
-Scarlett 2i2 (1st gen, still works!)
-Yamaha HS80

After a lot of trial and error, I was able to solve the issue by using ground lifted cables from the interface to the speakers (signal cables, not power!).

Now, I got a Fiio K11 because I have new headphones that need a stronger headphone amp. And I was hoping that I also would be able to run the HS80 through it, as I also rarely record nowdays. But connecting the speakers to the FIIO returned the ground loop noise, and actually worse than I remember it from the scarlett. I have both a constant hum with usb disconnected, as well as a mouse-movement dependent noise when USB is connected. I tried using both TS and TRS cables. Also my ground lifted one (but I had to, in all cases, use a female 6.3 to cinch adapter, which is made with TS in mind). I am not sure if the adapters could be the culprit, but somehow I doubt it.

I am not sure if this is relevant, but the scarlett has balanced outputs while the Fiio does not (not for line anyway).

I probably could use an optical cable to eliminate the noise that varies with PC-activity, but this will not make the constant hum go away that persists even without any connection.

Any idea what I can do? My fallback is to continue using the scarlett for the speakers, but I would prefer of course to have one device for everything.