That's mostly rhetoric.. The idmax is a high Q low fs woofer. That means it has a weak motor and soft suspension. It should give it a nice fat low end response in a mid to large sized enclosure and will move down low easily, that is what most people refer to as "loud without much power" the cone moves a lot on low power down low..
Anways the Fi Q is going to move less, your porting it. That reduces cone excursion. A high Q fi Q is basically an idmax, with a beefier motor, coil and more powerhandling and xmax. It will handle 1000 watts much better (right now your single handles 2k) and has 50% more xmax. The low Q one you have won't have quite a much low end as an idmax, on a watt per watt basis, but once you throw in some power compression I bet it's pretty close. Maybe the idmax v4's are better, but I know in all the previous versions, 1000 watts of power while "rated" was often asking for trouble and eventually led to coil rub. Since you can't give your idmax's the large box the really want to not need 1k to each, that may be an issue. Your box is fine for you sub, just realize you'll likely be able to run into thermal issues before mechanical.
Anyway here is another option to consider, I know I brought them up before. They are a very good value.. xmax is rated at 12mm, but that's geometric. Data-bass.com did a review and said 20mm was a much more reasonable number and only at 25mm did the drivers begin to make any noise. I know most dayton drivers that have been klippel tested end up with more xmax than they rate it at.. They also use triple shorting rings, AND have a bigger coil, yet rate their powerhandling as lower.. Guess who's overrating and who is underrating between ID and Dayton ???? Just guess! lol. Oh, and they are literally half the price of the IDMAX, 500 dollars for a 2.5inch coil and I am fairly certain they aren't using a shorting rings, if they are I can't find anything on it, and that was always a complaint on the IDMAX's in the past. Waste of money to get the IDMAX's IMHO.
If your going to spend 500 on a driver get something like an LMS-R if you want to have crazy excursion and low end, at least there your getting LMS technology and shorting rings.. As I said there is more good tech in the dayton driver for 1/2 the price. Output is going to be pretty close and the Dayton likes the box size your using more, SQ I'd put the money on Dayton every time.
Anyway here is someone using the Dayton in a 1.6 cube box, he loves it
http://www.hometheatershack.com/forums/sealed-subwoofer-build-projects/28373-rss390ho-small-sealed-1-6-build-finished-walmart-truck-bedliner-paint-2.html