Q: Why can’t you give a more specific maximum continuous DC current rating for the transistor based MIDI-Switcher board?

A: I do not have, neither can afford, the facilities needed to safely test a PCB to destruction through over-current. The MIDI-Switcher PCB uses 2oz copper pour (i.e. double the standard copper track thickness) and load current is routed through both the top and bottom layer in parallel to increase handling. The maximum continuous current handling of the board is therefore probably greater than the 5A I quote, but I will not vouch for it and leave it up to you to find out for yourself - if you need to!