If you have an early Metro-Plex (serial number 99 or less) and want to switch functions using a programmable/MIDI unit you need an adapter to interface the 5 pin footswitch jack to 1/4" jacks. I make these to order, based on which jacks you require.
Standard configuration is 5 pin to one TRS (for BOOST and MODE) and one TS (for LOOP). This is tested with BOSS ES5, ES8 units, RJM amp gizmo and with Bob Bradshaw rigs.
As pictured: separate TS jack for each function.