The ZCON as it currently sits would probably be too much for a full concave cap, I've never seen one and I don't know of it being tested, it could be made to work, but not at this point, in my opinion...
It can sway either way, the SA-8's are VERY impressive, and the DCONs are just as good, pick the woofer(s) that will work best in your available space and falls in your budget.
Then why do people insist on using the term when it has been gone over a thousand times bub? Because people like yourself still DON'T get it.
Do not tell me to leave as I have advice to the original poster, I told him there enclosure and installation is more important than driver choice...
Tell me what you think "SQL" means, because it does not exist. Sound Quality Loud is in your dictionary? It sure isn't in mine.
The enclosure and installation will play a much larger role in sub bass response than driver selection.