Not Enough Power? Or Knowledge?

First of all, your interior vehicle space really isn't very big - a single 10" or 12" would be fine IMO unless you're really looking for some bump.  I like the sound of a 10" better, you lose a tiny bit of the very bottom end, but in truth very few musical tracks have anything but secondary resonance that low and even fewer people's ears are good enough to hear it.  If you're going for purre musicality, stick with the 10", it's usually more accurate.  If you want to feel the power, go 12", it'll have more true output with the same wattage.

Second, and again IMO, placed head to head the JL subs are HANDS DOWN better than the Alpine, provided both are set up correctly in the right type enclosure.  I would go for a sealed box, no ports, but I'm partial to very tight, conservative & musical sound.  Ported will give you more volume, but it will tend to peak at a certain frequency & have more "boom."  You really need to listen to both to decide.  One of them will speak to you.  In reality, you can't go wrong with either Alpine or JL, but the JL Stealthboxes are very tough to beat if they make one for your truck.

Last, about power - how do you keep asking all the right questions?  Power ratings on speakers are tricky.  Here's the deal:  9 times out of 10 a speaker only blows because the amp is overdriven, not the speaker.  Remember Headroom, the peak output of an amp responding to music dynamics?  When that's depleted & the amp can't deliver enough power, it "clips," meaning (very oversimplified) it distorts.  It's these distortion spikes that will cook a speaker, not the clean power even if it's more than the speaker's rating allows.  I have a single 10" sub rated to 250 watts.  I run 400 to it, but it's very clean power & never overdriven.  4 years old, never had a prob.  My satellites are rated to 70wpc, I consistently send them 100+ (large class A amps), again no problems.  I largely disregard speaker wattage ratings because if it's respectably built, clean power up to sometimes twice the spkr rating ain't no problem.

Now the disclaimer - this isn't a license to get crazy with your gear, and I'm not responsible if you start a campfire in your car doors.  Just use your head & be sensible (don't run 1000w into a 500w sub, but 700's probably fine), and for God's sake turn it down if you hear distortion!  Otherwise your amp choices sound great. 

Enjoy it, if you get quality gear now it'll likely follow you car to car.  If you get the cheapo stuff, you'll hate it & replace it 8 times, ultimately spending way more than just doing it right the first time.  And when you install it, buy your wiring at Partsexpress.com for 1/3 the price of the shops.  That's another topic.

Hey, one other thing - reread your question (why didn't I do this in the first place?), that sub amp will send 500 watts into a single channel only.  You plug two subs into that channel, you'll cut the ohms in half (down to 2) and theoretically double the output to about 500w EACH, plus cut the headroom in half (that's bad).  That's 1000w of bass, enough to compete for most-ubsurdly-loud-truck award in your neighborhood.  It'll also completely overshadow the other speakers.

Go with a single 10 or 12 with that amp, it'll complement the other speakers well & you'll probably never max it out.  You could probably get away with the JL 250/1, tho you'll push that amp harder.

See that, anytime time you boil down complex subjects into a paragraph, you're bound to tick someone off.   Of course it's a generalization.  And of course you & everyone else has a personal story where the rules of *What's Typical* just don't apply.  The idea here was to make a lot of info digestable & not overwhelming.  A 12" moves more air than a 10", and therefore *usually* has more output.

And the only instrument I know that drops below 40 hz with a fundamental is a huge pipe organ.  What are those recordings using?  Particularly Alphaville? 

Well here's what I believe I'm gonna run at this time. The posts have been good to me (thanks all for the advice):

Tell me what you think; I'm looking for some opinions on the final call before I spend the bucks.

JL Audio 300/4 to Push the Door Speakers (75w RMS @ 4 @ 1.5ohm to 4ohm 11V-14.5v)

JL Audio 250/1 to Push the Sub (250w RMS @ 1 @ 1.5ohm to 4ohm 11V-14.5V)

This just brought up another speed bump/question. My head unit only has two preouts, front & rear. Once I add the sub & amp, how am I going to get the input for it? The JL 250/1 does have a preout on it for the next amp. My Alpine head unit says I can change the settings to leave the front preouts unaffected by the fader, so would I run the front preout rca to the sub amp, then from the sub amp preout to the front channel input on the 4 channel amp? And run the rear channel preout from the HU directly to the rear channel on the 4 channel. Sounds right to me, but need advice (as always). I don’t want to upgrade the HU at this point, I’m working up to a flip-out DVD multimedia player, so don’t want to cough up money for a new HU just yet.

I think I almost got it. Maybe.

About instruments below 40hz, that was actually a question, and the chart you gave was interesting - I've been educated today, thanks.

No.  What you've proven is that my generalizations are not always true.  That's why they're general, not hard facts. 

You've also shown that some bonehead is always going to take things personally and make it a mission to disprove them, ultimately confusing the issue & defeating the purpose.  Who the hell uses the last four keys on a piano anyway?  And who plans their speakers around that? 

Now that those issues are resolved, can someone send some advice my way on my last post? I understand I've had way more help than I probably should have, but let's get back on topic. Keep in mind everyone will have their own opinions and outlooks, and regardless, we are all here for the same, Car Audio Help! At least I know I am, I'm the newbie here!

I appreciate everyone's advice and words, I wouldn't know what to do without this site/forum. Heck, I thought I'd have a fight on my hands when I posted I was looking to stay with all Alpine, but people made some good suggestions and now I'm not cutting myself short! Opinions are good, and in this site several heads are better than one!