The ground distribution block is for adding a 4 channel amplifier in the future if you so choose to. You don't need to buy it now just save that link for the future then as those are always around.
Okay how are you going to hook up the subwoofers and amplifier then to the head unit? For a stock unit you need a LOC of some sort .You should get a quality LOC not some cheap walmart one.
This is a cheapo but a decent one as you want to have one with the adjustable on it.
NVX XPLOC4 • 600W 150W Per Channel Premium Super Low Distortion 4-Channel Adjustable Line Output Converter - for Adding Amplifiers • 4-Channel Premium Adjustable Line Output Converter • 6:1 Step Down With Adjustable Output • 600w Total Maximum Input 150w Per Channel • Super Low Distortion
www.sonicelectronix.com
These 2 below are the ones most people go to.
Audio Control LC1i • 2 Channel 400 Watts Line Output Converter • Adjustable 2-channel line out converter • Separate level adjustment for each channel • 400 watt maximum output • GTO Signal Sense
www.sonicelectronix.com
AudioControl LC2i - Black • 2 Channel Line Out Converter with AccuBASS • Two Channels of Active Speaker Level Inputs • AccuBASS Processing • 9.5 Volt Pre-Amp Outs • GTO - Signal Sensing Inputs
www.sonicelectronix.com
If you are strapped for cash then get the NVX at ebay here below. Same one as at sonicelectronix.
Buy & sell electronics, cars, clothes, collectibles & more on eBay, the world's online marketplace. Top brands, low prices & free shipping on many items.
rover.ebay.com
Sigh if you were closer and you could find a decent used head unit I would just show you how to do it. It doesn't look chunky and off when it is done right. Been doing this for 25+ years and only once did it look off and that was because I broke one of the taps on the install kit.
So you are going to have to order that NVX so you can wire into the oem wiring via high inputs and then the LOC is adjustable. Others here are better at that then I am as I haven't had to do that in over 20 years and that was for a friends car.