I have spectra 22s.
I did not buy the optional acoustat subs.
I understand that they were never anything special.
I will say that my spectra 22s do have a sub switch which I don't think a lot of other acoustats have.
Maybe 6 or 8 years ago I purchased a pair of martin logan dynamos.
Sometimes I have the dynamos switched in and sometimes I have them switched out.
The only difference that I can tell with the subs in is a bit more base "slam".
The acoustats are supposed to go louder with subs but this is not an issue in my small room.
Due to a problem with room node resonances, these day I have the subs along the side wall and I sometimes run the spectra 22s full range and the subs on as well.
I do think that a lot depends on the subs.
The subs need to be "fast", which I take to mean well designed to go with electrostats.
While I think that more or less any sub can be designed to go well with electrostats you probably have the best chance of a good match with sealed box type subs, e.g. my dynamos.
Just some thoughts.
Hope this helps.
Bruce