Electroid,
You may be mis-interpreting my comments. The rolloff of high frequency is on the power line, not on the reproduction of the recording. Yes, I can easily believe that if the RFI is reduced on your power lines that this would translate to a more relaxed and extended high frequency presentation without any rolloff. The removal of noise on power deliver is frequently described as translating to a "blacker" background on the music, which would allow a better presentation of low level detail and of high frequencies.