Truthfully, running conventional mode, you only have one engine in the picture on a particular power district, so 6A is more than enough. Since I just built mine for the workbench, I use junkbox parts, that was 3A diodes. Also, keep in mind that the diodes are only passing current in one direction, so truthfully the pairs diodes would be within their ratings with 6 amps of current in the circuit.
For your application, you'd run the power to each block through the box and then on the the track. That way each box would only affect that power district.
