Update on the two behringers.
After replacing the main amplification chip on the HA-8000 the result was... the same... what? That had taken some time because I had to desolder and remove the output jack to be able to get to the chip. So I did some more checking and dug up the pin config of the main volume pot. Desoldered that one too and guess what...
it failed. It's a miniature 10k stereo pot with a rather strange config (which is why I didn't catch the error first hand) and apparently one of the sliders hardly made contact. So I dismantled it, cleaned all the parts and readjusted the slider a bit. After putting everything together it worked again and so I soldered it on the main board again and tadaaa, problem solved.
I also double checked the MDX-1600 and cleaned sprayed all of the pots. After doing another checkup with the frequency generator and the scope it seems to work correctly. Both channels are doing exactly the same. I haven't check it with my gear as I still have nothing setup and you can't just plug a bass in as it needs line signals, so that'll have to wait a bit, but it seems ok.
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