Some of my Lp ( most of them are second handed) have a succession of tiny wavesYikes!
On these records of course the TP / Shelter still shakes but I think now that it is normal ... I only didn't hear it with the Rega /audio note because it was less transparent and perhaps (???) the TP/Shelter has less tolerance than the Rega / audio note when reading a bad record .Well, the TP is one of the great tracking arms, certainly much better than my OL Silver, which is similar to your Rega. But I don't have any records quite as bad as what you described.
The Shelter is quite new... but I effectively already think to go farther perhaps with a Zyx ( wich model to really feel a difference?) or the Shelter 90 X or a Koetsu ( Rosewood ) ...I don't know wich one would match the best the TPA ZYX is a better theoretical match for a TP than a Shelter or Koetsu. But it's also important to ask this: What kind of music do you play? Can you describe your sonic goals? What do you like best (and least) about your 901?
You apparently haven't heard a ZYX or Koetsu, but they are very different from a Shelter and also from each other. You will hear major differences between all of these.
You tell me that the Tp 's wire is copper , is it a problem if the two next modulation wires( From step up to preamp and from preamp to amplifiers)It's certainly not a "problem". It's just a matter of sound. I haven't tried all silver wire so I can't say what differences you would hear. Even those who have tried it might not know how it would sound in *your* system. With wire, tubes, resonance control, cartridge setup and other "tweaks", hearing in your own system is really the only way.
are pure silver ( audio note AN V).
Would it be better to have exactly the same wire ( discovery) everywhere?