Please don´t laugh!!! :)
I went back to my phono preamp and tried the 50 Ohm "setting", different presentation but still funny sounding. Then placed the DIP switched for 150 Ohms and, while different sound, still got a non-convincing result.
Then. I noticed that I was assuming (+) the positions marked OPEN in the DIP switch bank... called a friend and informed me that CLOSED is (+), not OPEN.!!!!!!
You were right!! 100 Ohms sounds better!!!!
Thanks for your help.
Fernando