fusionssl
yes you can damage a speaker by running it below it nominal power rating

That is a myth. Here is some info on what actually causes damage to speakers.
http://www.bcae1.com/2ltlpwr.htm
 
It mentions clipping at lower power as one of the main culprits to damaging a driver... The best way to avoid that is to tune your system with something like this:

 
I had one of those for my last set-up. It was really nice to get the maximum output of my system, knowing it wasn't damaging my drivers at full volume. My Pioneer unit didn't clip until 61/62 volume. I tuned my system at 60/62 with the SMD DD-1 and I used the sound quality tracks, rather than the power for loudness. It's definitely worth getting if you are going to run amplifiers.
 

Mkkari

Violence.
CDT makes some really nice affordable 5.25 coax sets that last forever. Had a pair in my s10. Things took a beating and never died on me. The classic series is what i had. 
 
Car audio once you get to a certain level is completly different then home audio. Once you get into competition style audio its a whole different world. Tuning frequency, Resonant frequency and all come into play. If going for sound quality alignment and all comes into play also. Most is vehicle specific. 
 
Ive been 158.6db sealed legal @37hz and 160.6 outlaw in the kick panel in my last truck. Working on a new build now trying for over 162db sealed up. 

Is there any info you wanna pass to me? I've been lurking into some 6th orders for a month now, its kinda closed area where isnt any advices around. If you dont want to, i can feel you.

 
really alot of people do not mess with 6th orders due to the tuning factors. It is tricky to tune a 6th order properly. 4th orders and flat walls are more popular with ported boxes being the most popular. If you are newer to tunings i would do a ported box first, if walled do a slot port. the tuning is easier. 4th order can be trickier to tune but way easier then a 6th order. My current build will be a 4th order bandpass build with 6 or 8 15's. Concrete enclosure floor, 2x4 subframe with 1.5" thick birch plys over top of that. Enclosure is all about being as rigid as possible. Flex in the box is a bad thing. I still have a lot ways to go on the enclosure. i have another 20 2x4's i will be cutting up tomorrow. ill have over 60 in this box
 

Violence.

Mkkari

Violence.
CDT makes some really nice affordable 5.25 coax sets that last forever. Had a pair in my s10. Things took a beating and never died on me. The classic series is what i had. 
 
Car audio once you get to a certain level is completly different then home audio. Once you get into competition style audio its a whole different world. Tuning frequency, Resonant frequency and all come into play. If going for sound quality alignment and all comes into play also. Most is vehicle specific. 
 
Ive been 158.6db sealed legal @37hz and 160.6 outlaw in the kick panel in my last truck. Working on a new build now trying for over 162db sealed up. 

Is there any info you wanna pass to me? I've been lurking into some 6th orders for a month now, its kinda closed area where isnt any advices around. If you dont want to, i can feel you.

 
really alot of people do not mess with 6th orders due to the tuning factors. It is tricky to tune a 6th order properly. 4th orders and flat walls are more popular with ported boxes being the most popular. If you are newer to tunings i would do a ported box first, if walled do a slot port. the tuning is easier. 4th order can be trickier to tune but way easier then a 6th order. My current build will be a 4th order bandpass build with 6 or 8 15's. Concrete enclosure floor, 2x4 subframe with 1.5" thick birch plys over top of that. Enclosure is all about being as rigid as possible. Flex in the box is a bad thing. I still have a lot ways to go on the enclosure. i have another 20 2x4's i will be cutting up tomorrow. ill have over 60 in this box
 

I look forward to seeing your build, if you share it on here. But man... nearly 160db's is just crazy. Even the enthusiast that I follow on the car audio forums barely break 150db, while only a handful break 160db. The OP is looking for tuning on an entry level system and you are over here trying to show him how to get close to world records lol

Violence.really alot of people do not mess with 6th orders due to the tuning factors. It is tricky to tune a 6th order properly. 4th orders and flat walls are more popular with ported boxes being the most popular. If you are newer to tunings i would do a ported box first, if walled do a slot port. the tuning is easier. 4th order can be trickier to tune but way easier then a 6th order. My current build will be a 4th order bandpass build with 6 or 8 15's. Concrete enclosure floor, 2x4 subframe with 1.5" thick birch plys over top of that. Enclosure is all about being as rigid as possible. Flex in the box is a bad thing. I still have a lot ways to go on the enclosure. i have another 20 2x4's i will be cutting up tomorrow. ill have over 60 in this box
 

 
I agree with RainStryke that you should keep us informed about this build. I've done just one 6th this year. It plays well with one 12", but somewhy im not impressed. Double bass goes little bit porridge, but you can feel it coming. Also in the other end 20hz is coming out with nice wind. Main peak is around 50's. Capacity 1:2 and ports 1:5. Going to get another sub for it and turn the power on. Now this builds been disassembled and we'll see about it next year when electricity is done well. This is just my shopping cart.
 
We'll starting friends build somewhere near this day. 4x 18" Sundown Teams with 4x Hertz MP15k's @ 18volts. Walled 6th.

Just an update, those NVX speakers came and they sound pretty good. I was a little bummed to find that someone already did some mod work and the speakers that came out were actually 6.5" Pioneers. I also found out that the one speaker was not blown but was just shorting out due to a bad wire job. The Nvx speakers sound better side by side. I checked them in and out and the nvx just sounded cleaner. I was actually surprised how much bass they had too. After checking polarity and doing some minor rewiring, I ended up pulling the stock speakers in the rear and putting the pioneers in there. I had to drill into the fiberglass panel and they only have 2 screws holding each speaker in but I just want to see how I like them for now.
   I also scored a roof rack so I can get my spare tire out of the back and I think I am going to build a small ported sub box for the 10" I have. After everything is kinda in, the system sounds leaps and bounds better than it did. Thanks guys!

Start of my enclosure. over 100 2x4's. Floor of the box is 3" thick fiber reinforced concrete. entire box is 2 layers of 2x4 thus far. Will be 2 layers of 3/4 birch ply on top of that. All corners rounded. Centered port. Subs will be in tubes. 4x15" subs is what I'm going with now. Each sub will be in 1.5 cubes per driver sealed. 4th order enclosure. Will be around 10k watts per driver. Straight SPL style build that should play music when done. All in a 1998 Chevy Astro van.