If the specs are accuarte then the DeCapoi dosen't go quite as deep in bass as your AE's. The DeCapoi is 42hz (+/-3db). The Decapo do have 8" woofers but they give up a few hz on the low end for better effeciency.
I really doubt if you'll find anything in a bookshelf that goes noticably lower then the 40hz you already have.
I run the Jungson JA88D with Eastsound CD-E5 along with Focus Audio FS688's. They are specs to 45hz but with the Jungson/Eastsound combo (both which are outstanding in bass) I have no complaints about bass in a room similar in size to yours. The quality in bass more then makes up for any lack of depth.
They sell for $3k but on rare occasion are available used on Audiogon.
BW MaxxC
I really doubt if you'll find anything in a bookshelf that goes noticably lower then the 40hz you already have.
I run the Jungson JA88D with Eastsound CD-E5 along with Focus Audio FS688's. They are specs to 45hz but with the Jungson/Eastsound combo (both which are outstanding in bass) I have no complaints about bass in a room similar in size to yours. The quality in bass more then makes up for any lack of depth.
They sell for $3k but on rare occasion are available used on Audiogon.
BW MaxxC