I haven't posted for a long a long time as I was basically on the road and had to put my turntable in storage. But it's been out for a week now and is running just fine.
I changed the resistors in my speaker crossovers from generic metall oxide to Mills wire wounds. No huuuuuuge breakthrough but still so much better that I had the feeling the mod was absolutely necessary not to limit the other parts of the speakers.

Don't use lead free solder. It's horrible.