noise ..noise..noise..

Sounds like power outlet,tubes or transformer noise by your description.Then again you might be hearing the difference in the preamp section's gain output relative to the amplifier's input sensitivity of the integrate.

In layman terms it's like having a preamp with too much gain for the amplifier.You get that background hiss in the music.With the volume turned all the way down it is very noticeable.

The watts have nothing to do with how quiet an amplfier is.
Some are just noisy no matter what you do.Especially on highly sensitive speakers like yours. I would really consider a battery based amplifier for that type of speaker.
It just doesn't get much quieter than a battery based power supply.

Greg ..it doesn't matter what line conditioner you buy. It will never be as quiet as a battery based power supply.
Apparently you haven't owned a very sensitive speaker. Some AC power based amplifiers have more noise than others but most do have some noise.You can put $5000 worth of cables on a big ass tube amp or SS with massive transformers on it. Hook it to a pair of 102 db sensitive speakers,and prepare to enjoy some soothing white noise or hum! The only AC power based amplifiers I've heard that are dead quiet use a muting circuit when no signal is present.This doesn't make them hiss/hum free when the musics playing though.