Thanks for all of your thoughts and criticism! Obviously, I described the project too superficially. The project is more about creating a proof of concept and learning something along the way. For my tests I always use a low voltage galvanically isolated 50hz/60hz sinewave, generated by an audio amplifier for safety. My first idea was to use a fully analogue system, because of its relative simplicity and latency. But I see your points concerning interferences and bandwidth problems. So, in the future I plan to go the digital way, as recommended from many of you. I plan to use a premade “ethernet over powerline adapter”, two Raspberry Pi’s and an USB digitizer. I hope that, I will have more success that way.
Thanks again to all of you, for taking the time to correct my ideas or provide new ones.
postscript: After a quick Internet research, it seems to me that USB digitiser are pretty expensive. Is there any way to built one myself, maybe with a universal Atmel microcontroller (With an SPI output? Or are there two slow?)? Or are there more operational specific IC´s for that purpose?