I have tried a few different approaches to ionizing treatment. All produced an effect, some good, some not so good.
Picked up several tourmaline crystals at a flea market (each about the size of a hens egg) for ~$6.00. These generate negative ions when heated. Placed these over the power tubes on my amp and heard a small change - cleaner treble, but also colder and a bit harsh.
Tried a consumer type room ionizer, heard open relaxed, detailed treble - very complimentary. Later tried pointing the ionizer directly at my components (on highest setting) and got more detail, but that cold hard treble was back.
IMO - it works. Just need to find the right balnce, setting, room position, etc.