I use Sort Kones on my phono preamp, preamp and amp. They do make a difference. I would describe it as cleaning up minor distortions and noise artifacts which improves the transparency of your system.
If you look at the Nordost information on Sort Kones they describe the effect and reasons for the improvement in more detail.
If you look at the Nordost information on Sort Kones they describe the effect and reasons for the improvement in more detail.