Good evening wapehatson,
I live in Germany and here I found a gentleman named Ralf Kassel. He‘s a development engineer for some audio brands and beside that he‘s very experienced with all sorts of Spectral gear. First he removed the strange addition to the power supply of my unit. Then he changed all capacitors and finally he reduced the gain of the unit. He explained to me that lots of preamplifiers of that time had a much higher gain, than todays units. That high gain is not needed with todays sources. After all the corrections he made a complete assessment of the DMC-12 with Audio Precision and Neutrik equipment And documented it. The unit performs now absolutely flawless and as good as at it’s day one. If at the end the reduction of the noise level came from the change of the aged capacitors, or the reduction in gain, or the take out of the unnessesary modification to the power supply is hard to say. I would assume it was a combination of all. I am using also high efficient loudspeakers (JBL 4333B) with the DMC-12 (although not that efficient than yours). Noise is no longer problem to me. I have attached the measurement document and an inside view of my unit.