For any type of musical application it simply is not worth it.
If your going for a 15dB peak at 1 frequency knock yourself out..but that is not what music is about (Which is what 99% of people who buy subwoofers, buy them for..is music) The rest are the hand full of dBdraggers that run the woofers, and nobody really cares about that any more. There are no people there so there is no point even trying to enter the market of an 'spl' woofer.
It's not about efficiency, as a whole subwoofers are terribly inefficient as far as taking electrical energy and transforming it into acoustical energy (5-7% efficient at BEST). When you make a woofer with such a low Qts and a very high Bl your going to have a HUGE peak in frequency response, which is great for burping in SPL. However with music, not so much.
At the end of the day It's all about the music, simply put if you want to have musical output with a DD sub you'd be far ahead of yourself to save the money and go with a 9500, or a 9500 i guess with the Kevlar cone if you feel you must have it...or one of the lower series of woofers.
The Z is nothing more then a conversation piece or a flagship type deal to get people to talk of the brand...seems to work pretty well. It's not practical for 99% of most users though. But some will buy it and swear it is the greatest thing since sliced bread, justifying the money that they spent on it. I can't lie, I would too. $2500 is a lot of money for a speaker that musically speaking isn't worth it...you could have 5 or 6 9500's for the price of 1 of the Z's..and absolutely destroy it in a daily driving / musical scenario.
