A little more info on my purchase.
The BL3500 is an MK1 with the MCL connector and SW 1.2.
The black box is another 1611 converter
I already tested the BL3500 with a minijack to MCL connector special cable, and its working fine so probably ready to go into the testing setup.
I dont think I realised before how the function with the Menu 0 4 GO is so easily aborted with any button press, so I really understand how its not an optimal way to use it.