According to ZKIT1 Assembly Instructions in
https://www.decware.com/newsite/SE84CDIYINSTRUCTIONS.pdf :
"To series the outputs, hook the left channel negative to the right
channel positive with a length of wire. Use the remaining posts to drive the loudspeaker."
So I guess your drawing is showing a series configuration.
Also, don't forget to also bridge the inputs, for example, using an "Y" RCA cable.