fi car audio and soundsplinter

I run the rl-p 15's and am quite happy with them.  The customer service is second to none which is always good.  I must say you are just a little late for the rl-p cause the price took a hike along with the tcsounds stuff (whom soundsplinter gets their motors from).  Still a great value though.  I've always heard good things about the Fi stuff as well.  If you want to be really unique check out the soundsolutionsaudio.com icon driver as well.

As a side note, and keep in mind i have virtually no experience with the w7, i'm not sure the rl-p is going to drastically outperform the w7 in any way just from reviews and things i've seen online.  If you're just bored and looking for a change it would be worth giving them a go for sure though.  Hell you might be able to get a new rl-p with money left over after selling the w7 too.

I'm not too familiar with Fi, but I know Soundsplinter makes a fine sub along with being a great company.  The W7 will have lower distortion than anything they have, but output should be similar.  The W7 was designed to get the best performance possible with no reguard to price.  It utilizes machined parts and expensive tooling to achieve that goal, hence the high price.  Sure you can make compromises get close to the same performance in a cheaper woofer, but some people don't want compromise; they want the best.  There is a reason why the W7 is the reference people compare subs to.

So, what are you trying to achieve by making this change?  Are you sure changing the subwoofer will get you what you want?  Maybe a different enclosure might be a better way to go.

Anyway, if you still are looking to change subs, then I will also suggest looking at this sub:  http://www.diycable.com/main/product_info.php?cPath=24_93&products_id=653  It will have the same super low distortion and output capability as the W7, but with a MUCH lower price tag.  The downside is that it's not as "pretty" as the W7.  Another difference is that it trades enclosure size for efficiency.