The problem with upgrading components in a Jadis piece of equipment is that the company really designed a lot of its models around the component parts they use in them, particularly the older units. When you start to modify it, you can put in capacitors, resistors and the like that are "better", but the resulting sound won't necessarily be a Jadis. Many of the modifications done back in the 90s were like this; at least one of the regular posters on these forums had some mods in a used unit he purchased un-done because it was not the Jadis sound that he was looking for.
The only mods I made to my Jadis JP80 and JA80s were done by Andy Bouwman of Vintage Tube Services, back when Andy was doing his "Romantic Era Treatment" modifications (I don't think he does them anymore). These were the only mods I've heard to the equipment that managed to keep the Jadis "sound" intact--in fact, they probably made the sound even more luscious, grainless and natural. I also did have Andy put in some Audio Note silver oil capacitors as by-pass caps in the preamp, and some vintage oil capacitors in the amps; we liked the changes made by those (one listener remarked that my JA80s as so modified sounded as close to SETs as a push-pull design could).
So you can mod, but at your peril. I would go for capacitors like the Audio Notes if you want to try that, because Audio Note parts tend to be consistent with the Jadis sound. And you can always try some tube-rolling to change the sound of the units. If you want more detail, sheer transparency, dynamics and hi-fi thrills, though, I'd suggest using a different brand of components entirely.
The only mods I made to my Jadis JP80 and JA80s were done by Andy Bouwman of Vintage Tube Services, back when Andy was doing his "Romantic Era Treatment" modifications (I don't think he does them anymore). These were the only mods I've heard to the equipment that managed to keep the Jadis "sound" intact--in fact, they probably made the sound even more luscious, grainless and natural. I also did have Andy put in some Audio Note silver oil capacitors as by-pass caps in the preamp, and some vintage oil capacitors in the amps; we liked the changes made by those (one listener remarked that my JA80s as so modified sounded as close to SETs as a push-pull design could).
So you can mod, but at your peril. I would go for capacitors like the Audio Notes if you want to try that, because Audio Note parts tend to be consistent with the Jadis sound. And you can always try some tube-rolling to change the sound of the units. If you want more detail, sheer transparency, dynamics and hi-fi thrills, though, I'd suggest using a different brand of components entirely.