Considering XXXs and Brahmas are built at the same place, by the same production line, perhaps it's more a reflection of the numbers of drivers sold?
Brahmas hold together VERY well... Even in really high power applications, if used properly - witness Scottie Johnson with 10KW - yes, 10,000W - per driver, or Scott Stoner with 8 KW to each unit, and on and on...
A subwoofer is like a car. A high performance subwoofer is like a high performance car. Just because you buy a Ferrari 355 doesn't mean you can drive on like Michael Andretti.
Just because you buy a high performance sub doesn't mean you can run it like Scottie Johnson, Scott Stoner, Bob Beatty, etc.
Experience is what makes the difference. Starting out in your audio world with $400 subs and $500 amps isn't really a good way to go. Start lower, learn how it works, then move up.
Dan Wiggins
Adire Audio