According to the ATC SCM40 manual, when ATC mentions bi or tri-wiring they are actually referring to bi or tri-amping.
ATC Entry Series monitors are equipped with a “bi-” or “tri-wire” connection panel that enables separate amplification of the bass/mid driver and tweeter. Remove the linking bars between the pairs of terminals if you wish to take advantage of this facility.
The pairs of binding posts are laid out to match the drive unit positions with the bass driver pair towards the lower edge of the input panel. Ensure the multiple amplifiers used for bi or tri-amping have equal gain and use the most powerful amplifier for the LF driver.
You should be able to tri-wire if you so desire but you would probably have to build your own cables. This could easily be done by using six individual speaker cables terminated with stackable banana plugs on the amplifier end.