all the cables of the Sme should be replaced obtaining a direct line from the head to the phono preamp without joints. LoL
Does "Lol" mean you’re joking? I’ll pretend you’re not, because I've rewired 3 arms, in the way you describe, and all 3 were much better for it.
I had a SME 309 and wanted to rewire it straight-through, as you propose. Reason: I had an Ittok before the 309, and my new 309 was so clearly better I retired the Ittok.
I also had a Syrinx PU3, and unlike the Ittok, it was clearly better than the 309. (Using the same cartridges one each, of course). The Syrinx is wired without any breaks: is that why it sounded better?
To test the hypothesis, I rewired the Ittok, directly from cartridge-pins to preamp-RCAs, without a single joint. To my surprise, it now surpassed the 309, and it was more than subtle: it was not confirmation bias.
So logically rewiring the 309 would yield the same benefits. I called SME, and they warned me not to. They didn’t argue arrogantly that it was "perfect" and who was I to question their mastery? No, they just said it was impossible — because a) there’s not enough clearance between the parts to feed the wire through, so I’d have to take it apart; and b) putting it back together could only be done at the factory. It required special tools, and super-fine tolerances. I couldn’t do it myself.
I studied the 309 closely and they were right. I did the Ittok fairly easily, and two other arms — but the 309 would challenge even NASA.
End result: both the Syrinx and rewired Ittok were better, so I sold the 309. I hated to, I loved the look and feel of it, and obviously it’s a very good tonearm — just not as good.
It does have many breaks in the line, and I’m sure it would be better without them, but it was beyond DIY abilities.