Gyrodec Best Tonearm

If the Zeta is working well, keep it. Change for change sake is expensive and unproductive.

I prefered Zeta on the Linn LP 12 above FR-64 mainly because of weight. Though Zeta is also a 'heavy gun' .
This 'factor' is related to the used springs. On Thorens
160 Super the Alphason HR 100 was a better match.
Your own idea to send the arm to Johny of Origami is the best of all propositions. Your problem is the cart not the
tonearm. The Ortofon Kontrapunkt C or Jubilee are much
better. If you intend to experiment with MM carts then
the Alphason is the best choice. On ebay the Zeta is slightly more expensive. I assume of course that the money
issue is important.

Regards,

I'm currently using an Ortofon Cadenza Black cartridge and it sounds wonderful on an Ortofon AS212S tonearm, not quite so good on an SME IV tonearm with an uncomfortable peaky treble. This is mounted on an SME 20/2 turntable.

Instead of upgrading your tonearm, have you considered upgrading the Gyrodec with updated power supply/bearing/platter ? You might get a bigger return from power supply upgrades and or an overhaul of the Zeta by Audio Origami - bearing check and rewire.

Dover, First thing first. Think of all those Linn-LP 12
mods. They are 'countless' in the meanwile. Do you want him
to enter this 'labyrinth'? Nice to see that you know about
Origami. The only problem with Zeta I know of are the bearings. A peace of mind has also value and this Johny is
a decent guy. So if the bearings needs correction he will
do just that. I myself am very skeptical about rewiring but
this is also an option. Johny will never advise with the intention to earn money. I am sorry for you but my advise is much better.
Regards,