It took me a couple of tries but I did get two consoles connected with 3.5mm cable and jacdac. BrainPad Arcade to Meow bit. I did install the new bootloader into the BPA, thanks Greg for that. I’ll do a good video about this soon, just wanted to let you guys know that it seems to work (with some quirks): https://youtu.be/iofADeGRXTA Button presses on one console controls sprites on the other. I have not got this to work with Pong yet but it could be the old bootloader this morning confused the consoles.
By the way, keep the video link on a separate page and it will get embedded in the post