Because I have incredible quantities of RFI/EMI interference where I live, I had clip on ferrites on all power & digital leads none on phono leads, on the advice of HD Music & Test I removed them from all digital leads which was literally a revelation. On the advice of MartinT I put these spare ferrites on to those Switching PSU's that I have not swapped yet for Linear PSU's & I have also put them on all of my power leads even though copper  foil shielded, this has resulted in a vast reduction in interference, the system sounding better than ever before.