Tony, I have the very same diffusers from PI Audio Group. Indeed they come in 2 pairs, one female and one male to each pair. I bought mine unpainted, and did them myself with 8 coats of paint....the paint was an eggshell finish, and mixed with classic Elmer's glue as a hardener.
lazb has a very similar treatment setup as I do, on the front wall....in his case its 1 full set [2 pairs].
I can tell you they are extraordinary and far more than worth the cost. In my small 12x10 room, I have discovered them to be absolutely critical, part of an overall approach. They cause much more clarity and rid the room of muddiness, flutter echo. These, coupled with good carpeting on top of rubberized "waffle" padding [can be hard to find] make all the difference, changing the sense of air/spaciousness and soundstage to more akin to that of a much larger room.
I very highly recommend you contact
Dave at PI Audio.
https://piaudiogroup.com/Brad