Well output is easy right? All I do in my installs is to use lots of large subs to fulfill the requirement. Getting a low distortion sound is far harder. You can't quite double up on drivers and lower some sorts of distortion. There are all sorts of benefits from having lots of copper in the motor that go beyond extending bandwidth.

Since the AE subs are very high sensitivity the increased xmax on the FI should have negligible benefits. How low do these actually equal eachother in output? 30HZ? Then there are heavy AE subs that have more output like the AV series.

The AE imo is unrivaled. The FI however does have fierce competition. Why would you ever get the FI over the CSS? Not all xmax is created equal, the CSS will have a very flat BL by comparison AND shorting rings.