Having one of the 2 cables I decided to copy it to make myself a second one.
There is 6 distinct wires per cable and I think it shouldn't be too difficult to find a similar cable.

Servo-sound cable

But the proprietary connections (male and female) need to be reverse engineered.
Both connections are strictly identical and made of 4 different parts that shouldn't be difficult to 3D print.

Servo-sound connection

So I started by designing the 4 parts back from the original cable using SketchUp.
This was quiet easy and pretty fast to do :

Servo-sound connectionServo-sound connection

Next step will be to print them and check if they can fit together. But I'm confident they will.
ATM I just don't have the time to print them but I will soon show you how it's goin' on... and will tell you how this legendary vintage hifi sounds like.

Edited :

Done. I finally got the time to print them and I'm very satisfied with the result.
All the parts are fitting perfectly well and all I have to do now is find some copper and do some soldering.

Cable end_printed Cable end_assembled

I also decided to improve the design to ease the printing process.
For the cage part (the biggest one on the right) I decided to print the small part that is at the bottom (when printed) separately to get a better printed surface quality (no supports). The small part (shown white below) will then be glued back to the cage with acetone, which won't be noticeable on the final design.

CageV2

For the small part that holds the cable in place (second one from the right), I decided to replace the 2 very tiny hooks that were too fragile by 2 holes in which I will glue 2 small pieces of 1.75mm diameter filament that won't be prone to break as easily.

BlockerV2

But I also found out that one of my 2 speakers doesn't work, so even when I will have my new cable ready to go, I won't be able to listen to it without having it repaired.
Or to repair it by myself but the problem is that I don't know much in electronic...

To be continued...

Note : you can already order a good quality print from Shapeways if you need to build your own cables.