The XD600 might be overkill, the XD300 is what JLA recommends in the doc:

http://mediacdn.jlaudio.com/media/mf...pdf?1474477807

Yes, and then also no. It somewhat depends on the rest of the system and how you intend to use it. A bigger amp, like a 500w that's undergained to 300-400w rms will run cooler. More expensive amps usually have extra features, like crossovers, preouts, etc, power management profiles for high heat to cool off while still playing, short protection to keep things from letting out the magic smoke should the worst happen... Etc etc. If you are planning on running on the stock head unit with a loc (line out converter) you need an amp with built in crossover. Many have this, but they differ and there in prices differ. I have an aftermarket head unit that controls the sub amp, and use a basic 500w alpine that just does what the head unit says, no logic in the amp setup.
Does that help?

is there any benefit of getting the xd600 over the xd300? sorry I know absolutely nothing about amps and subs. Im going to get it professionally installed but I just want to make sure I buy the correct products and high quality. The only reason I ask is the the xd600 is only about 40 bucks more than the xd300. Im willing to pay that if it means its an upgrade in sound quality. But i dont know if like you said, its overkill. I know the xd600 is a higher wattage than the xd300 does that help in anyway or does it now make a difference on the sub?

For $40 more? For one 400W sub it is overkill but for that minimal amount more will provide some additional overhead and as Chimera mentioned won't have to work as hard.

If you don't mind spending the extra $40, go for the bigger one and under gain it, affords you opportunities/flexibility to potentially reuse it in another car/application someday too potentially.
Also, I looked at the XD amps before going with the Alpine, they are nice and very small form factor, the Alpine is slightly larger physically. I have mine tucked under the trunk floor on the opposite side of where the factory amp goes, same side as the sub itself, it fits there very nicely admittedly, but if you were thinking of mounting the amp somewhere where it has open access to air (better cooling) then smaller is typically nicer.


Edit: if you do buy the larger one, make sure to tell your installer that you want them to use a DMM (digital MultiMeter) to under gain it. 400W RMS is what the speaker is rated for, 300 is recommended, you can go above that too depending on your settings. I have mine setup for 400W@ 75% vol on my HU using a 0db 60hz test tone. TBH this is slightly conservative, almost nothing music wise will actually play that way, but it suits my needs very well.

Viabox instead?
 

I recommend using viabox instead. They offer the cheapest shipping fees & are much faster - orders are processed to ship within 1 day. Hope this helps.

Sooo is anyone completely happy with the bass production from the JL Stealth box? I would like to buy it, but I am seriously considering a ported/fiber glass custom design in the driver side back seat door panel.

It hits extremely hard. A lot more punch and impact than the OEM Audio + sub. @HLUCIANO55 can tell you more he just installed it.

I'm very satisfied with mine. I have it running crossed at 63hz -18db recently.

I've been running the JL Stealthbox for over a year. I was ready to pull the trigger on OEM+, but feared the bass from their 8" subwoofer would not be enough for me as metal and electronic genres are my go to. I'm also running a Ca-Fi Dashlinq which lets me fine tune the sound.

Overall I'm very happy. The bass hits so hard that I had to install sound deadening at key places to prevent rattles - which I don't blame the subwoofer for, there are definitely locations on the rear of the car that can be prone to rattling without attention. At the moment, no rattles, the trunk doesn't shake, and August Burns Red has never sounded better.

The metal cover on the subwoofer is also a plus as I'm a total savage and transport my mountain bike in the trunk. I would like to upgrade the speakers / amps at some point but don't know where to start there.

Anyone have updates ?

on what? it fits, it booms. what more can you ask for?