I have now decided to go for one box instead of two connected by an umbilical cord.
This means I don’t have to try to put a big connector on the PCB which was proving difficult; getting the tracks past such a big connector at the edge of the PCB was very problematic.
But now the Power Supply Unit has to go within the same box which means fewer batteries but that shouldn’t be a problem at all, the ones left should be more than adequate for hours of listening. The problem now is how do I squeeze the PSU into this single box? Before, with two levels of batteries everything worked out perfectly – dimensions, interconnections, spacings. Now it’s all gone to hell!
This ‘system engineering’ problem is solvable but will take some thinking through while I reposition everything and work out the best way to now connect parts. It will mean I can star connect everything more easily using wires instead of the copper track on the PCB.