Internal rewiring of Parasound Halo A21 120V --> 230V voltage conversion

Hello everyone,
I recently acquired a gorgeous Parasound A21 which I imported from the US, and as I am really into DIY and opening things to check how it's made, I deliberately looked for a 2nd hand amp from the US, so I would have to switch the voltage operation by myself. I believe I have almost solved the problem, but considering the different sources I found online (none were exactly for the A21, rather for A52), I came to doubt the final moves.
The circuit board is a B4170A, I have already moved the jumper cable JP13 to JP14, the former being for AC120 V and the latter for AC230 V.
Now I'm facing the change into the big transformer wiring. I have a red wire on P4 and a white on P1, both connections labelled as AC120V. The target connectors are P5 and P6, labelled as AC 230V.
The last two transformer wires, yellow and black, are plugged onto "To Transformer TP12" and "P3" respectively, along with a "AC120V" written above both.

There are 2 more wires, P2 and TP11 which connected to the external fuse. ( I have already swapped it for a 6.3A slow blow one)

I know that for 120V operation, the transformers are connected in parallel, and they must be linked in series for 230V operation. The thing I do not know which one exactly are primary and secondary and all the cable are pretty well coated with plastic and I'm not sure how could I do an efficient continuity test.

I believe that I should plug P4 to P5, and P3 to P6. Does anyone know exactly which cable must be switched to please ? Also, I think I could/should change the internal fuses but I have not thought about those yet...
As a safety measure, I have created a power outlet linked in series with a 500W incandescent light bulb, to avoid surge on the A21, if I would come to mismatch some cable, which I'd rather avoid, thanks to this forum hopefully.
Thank you all for reading and hopefully understanding my issue, I wish you all a very pleasant day !
Zeka