EclaireXL

Have you seen the two pole pin header on right side of the sub board? Is for this exact reason.
You must make first a small coaxial cable ended at both sides in a DuPont connector, as to interconnect it with the corresponding one in the main board. You can find this as a three pole pin header, behind the audio stacked connector.
We choose to proceed like this, to avoid the unwanted digital noise within PCB.

This is only in v8 too

@Nir
As for the XC12 tape corder, just now I see that it haven't a PSU, so must take their power supply entirely from eclaireXL board.
This mean that you need to supply the eclaireXL with a power adapter of 1 or 2A. I don't know how exact is the percentage of the current who need the internal motor of XC12 to work.

I think this explain why eclaireXL resets it self when you push the "PLAY" key on this specific peripheral.

or i will build a cable are test, thanks

Nir