No electrical mods needed for the KT66 tubes. I have been running them in both Io power supplies for many months, and I leave my units on 24 hours a day. One warning, the KT66 tubes are too tall for the cover. Listen first, and if you agree with me on the sound, two holes must be punched in the lid to allow the Genelex to clear. I can advise you of a metal shop, or tell you the punch size. Using two power supplies does require circuit board jumpers in the main unit. The power supplies themselves require no additional changes. Jim White has a diagram and jumpers that he can send, provided that you are handy with a solder gun. If not, you can return only the main unit and get the jumpers soldered in. On improvements, I was undecided on the Io when it was stock. My Elliott Magnum Opus Phono was better. After changing out all the Sovtec tubes, I thought the Io was better. After I changed to two power supplies it was no contest, against anything I have ever heard. And when I replaced the EL34 the first round, I choose Tung Sol 5932 and then, after the twin power supplies, went instead to the KT66 Genelex. The Genelex is almost as much of an improvement over the 5932 or 6550 or 6L6, that it is like you went from the original Sovtecs to the NOS I am speaking of. One other thing, replace the input and output wire between the rear panel jacks and the main board. This is huge in reducing distortion and improving resolution. Pick the wire you like the personality of, but the best quality you can afford and can work with. I picked the conductor from Purist Audio Dominus. You can e-mail me, and I will give you my telephone number if you wish to talk. Or, we can communicate via e-mail, as you wish. Oh, almost forgot, I have no experience with replacing the caps, so I will not comment on something I have not tried.
