So here is how I see it :
Obviously 2 DBD boards with each its Tap tempo one
Both tap tempo boards (TTB) connected to the same Tempo clock stomp switch
Left DBD/TTB with no additional toggle switch for 1/4 note scale
Right DBD/TTB also with no additional switch, but tempo scale wired for the center position, ie dotted 8th notes.
Does this make sense to you ?