Well, that's good that its not the speakers.
It is extremely rare to have digital overs (over modulation) on a big label release. To check, you can rip it to a WAV file, then open the wav with Audacity (free download audio editor), and look at the waveform where you suspect the overs. They will appear as flat tops where the peaks hit the limit and flatten out.
If it were overs you would know it, it is like a SS amp clipping, not subtle. And it also happens only at full scale digital signal. The music you are listening to has decent dynamic range, so overs would only happen at the very top of the dynamic range, at the very loudest peaks. I'd be surprised if any Fleetwood Mac CD has overs on it. That is the worst kind of amateur mastering mistake.
What kind of distortion is it, what does it sound like? What frequency, mids, highs? Does it correspond to the music, or random?
Sounds like you have replaced everything in the whole chain? Amp, preamp, source, speakers, media. Next check wires, power filter, whatever. If there is a bad connection a microspark on peaks can make bad sounds.
Is there any right / left pan to the distortion sound, or is it centered?