Reddit mentions of Rockford Fosgate P300-12 12" 300W Sealed Powered Subwoofer Sub Enclosure+Amp Kit

Dash Kit
http://tinyurl.com/zs7jw9a

Head Unit
http://tinyurl.com/zlmsgku

It says this one comes with Lollipop, mine actually came with Kitkat. So I had encountered some things that I figured I'd share with everyone from my journey on this damn thing. I tried both the "knobless" version that I have now that came with KK, and the "knob/button" version that came with Lollipop. The Knob version was PAINFULLY slow, and pretty much unusable. I ended up returning it for the no knob. The Kitkat one is so much lighter and faster. The Kitkat unit also produced a buzz/hiss whereas the Lollipop unit did not. I replaced it with a 2nd Kitkat unit and it did the same thing. I tossed in a couple ground loop isolaters and it fixed the issue.

There are also custom android roms by a guy named Malaysk on XDA you can load onto these, which I highly recommend doing. It fixed a lot of weird bugs I had on it. The biggest being that Bluetooth calls only came through the right speaker??

As far as the wheel controls, the unit supports them, I haven't gotten them to work yet.

I had the upgraded audio system. I pulled out the amplifier that came with the car and replaced it with a http://www.rockfordfosgate.com/products/details/p400x4

I also replaced all the speakers with
http://www.rockfordfosgate.com/products/details/p1650 (for back speakers)
and the 6.5 version of
http://www.rockfordfosgate.com/products/details/p16-s for the fronts.

I also put in a
https://www.amazon.com/gp/product/B00IMNY6AW/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
for the sub.

I am super happy with the results, the audio is phenomenal.

Honda and budget upgrade don't really go together. The dash kit you linked to relocates the radio below the A/C controls, and your old radio remains above in a dead state. If you're not OK with that, there is another dash kit that recreates the HVAC controls to be above the radio, but it's not cheap.

If you have steering wheel controls, you need a smart harness from PAC to retain steering wheel button functionality.

That head unit is not the right one for you. It only has a single pair of RCA outputs, which is not enough for the direction you are going. Try this one instead, it has six RCA outputs. https://www.crutchfield.com/p_130X6800BS/Pioneer-DEH-X6800BS.html?tp=5684 If you can sacrifice a CD drive, you can get this one that has 4V preamp outputs to give more signal to your sub. https://www.crutchfield.com/p_130S501BS/Pioneer-MVH-S501BS.html?tp=5684

If you are on a tight budget, consider an amplified sub enclosure like this: https://www.amazon.com/Rockford-Fosgate-P300-12-Subwoofer-Enclosure/dp/B00IMNY6AW#customerReviews

With a sub, you'll probably want another amplifier for the new front speakers. Although you can try running new speakers off deck power and see if it works for you, then upgrade later.

TBH, replacing a working factory subwoofer with an aftermarket subwoofer usually isn't worth your money and time. If the factory subwoofer is rotted to hell and buzzing, sure, I get it. But if it's working, leave it or go full aftermarket amp and sub. The factory sub is high efficient, tuned for that application and power level. Plopping in a heavy power-hungry (by comparison) aftermarket sub isn't going to be an improvement.

Lastly, you'd also need to know the impedance of the factory subwoofer and match the aftermarket woofer to that, if you want to use the factory amp. Some factory subs are 8+ ohm or as low as 0.5 ohm. This is hard to get in the aftermarket world.

If you want more bass in a small compact package, consider adding in a small powered subwoofer. or option 2