Power can always be a problem but its more so the airspace for the box that can cause woofer failer, a great box is the key to great sounding subs. Believe it or not, 90% of the time when a speaker is "blown" its because it was under powered not over powered, granted if you run 2500watts off true power to a sub rated 300watts you'll prob have an issue. The less power that is run to the coil the harder it has to work to produce output therefore the hotter it gets, leading to the wonderful burnt coil smell, kinda like running a motor with little to no oil. Was that a single or a dual voice coil woofer? 2ohm or 4ohm? I'm wondering if the listed power was dynamic for 2ohm and you were running a 4ohm load(half the listed power) and it was a problem?
The suspension in a subwoofer needs the proper airspace to load and function correctly or you will over drive the sub causing it to fail. As box types and power handling is concerned they have nothing to do with each other at all, if any thing its requirment of more power. See a ported box will play "louder" at the tuned frequency, ie 35HZ so it will be 3-6db louder than a sealed box with the same amount of power, however it will be boomer sounding depending upon the tune and the woofer. A sealed box will typicaly be a tighter sound but again it will require twice the power to be the same volume out put. To gain a 3db increase in volume you must double power.
As far as your 6" mounting depth goes, there are a bunch of woofers on the market that will fit, you must also pay attention to the airspace requirements and box specs for the woofers. I have 2 10" Infinity Kappa Perfect VQ woofers in a ported box in my RC, fits perfect. The VQ are nice because you can alter the Q of the woofer which allows you to finely tune the woofer for the box your using.
Bottom line is what type of sound are you looking to acheive? Hammer you in the chest bass or a nice smooth bottom end? That will depict the box type to use in your install and woofers.
