So the culprit is either the Jadis or in the Meitner gear.
400 hours is nothing as far as tube life is concerned and in my experience the KT90s are very reliable. You also said nothing about your tubes not glowing right. For example bright fireworks in a KT90 at switch on, an abnormal brightness in the glow of them, or one of them being just dead below a sort of silvery veil on the glas. So I'm beginning to doubt, if the fault is in the tubes at all, but I'd still try a replacement set for good measure, which you could then keep for later use if the trouble is elsewhere. Do you have the chance to try another CD player? If the distortion stops, you have the culprit. If not, its the Jadis, unless your speaker cables somehow don't work well between the Jadis and your transducers. I'd try another set and listen, but I doubt, that the trouble comes from there. Good luck!
400 hours is nothing as far as tube life is concerned and in my experience the KT90s are very reliable. You also said nothing about your tubes not glowing right. For example bright fireworks in a KT90 at switch on, an abnormal brightness in the glow of them, or one of them being just dead below a sort of silvery veil on the glas. So I'm beginning to doubt, if the fault is in the tubes at all, but I'd still try a replacement set for good measure, which you could then keep for later use if the trouble is elsewhere. Do you have the chance to try another CD player? If the distortion stops, you have the culprit. If not, its the Jadis, unless your speaker cables somehow don't work well between the Jadis and your transducers. I'd try another set and listen, but I doubt, that the trouble comes from there. Good luck!