8 gauge for the power wire

 

Mhm
After reading, you have numerous problems with your setup
1.) Your head unit does not have a subwoofer RCA output, which although isn't a bad thing, they are not designed to carry only sub bass frequencies, therefore your subs are playing everything, and have no increase voltages on sub frequencies.
2.) Your amplifier is a 4 channel. Most anything that is not a class D, or a mono amplifier, is not a good choice for your subwoofers.
3.) Your sub setup, you don't seem to know what your sub ohm ratings are, whether or not they are hooked in parallel or series inside the box, or whether they are single or dual voice coil subs, and this in itself is probably the biggest issue.
4.) You have it hooked up to 1 channel on a four channel amp, not even bridged, which immediately will lack power. I am also fairly certain, that if you do bridge it, you will blow your subs. Judging by your subs currently getting about 150 watts both, and you say they get somewhat boom cranked, probably means they are running at a decent ohm rating, but without enough power. Therefore, by bridging it, you will probably drop it below 4 ohms, and potential burn your subs coils and blow your amp.
Do NOT bridge it, until you know what you are doing.

First thing first, in order of most important
Open up your box, see how the subs are wired, what the subs impedences are, and if they are single or dual voice coil

Secondly, it would help if you got a different amplifier, one that is designed for subs, therefore a class D and monoblock, although there are class D 2 channels, but mono block that can take down to 1 ohm would be best for now, but not until you find out the first issue

Thirdly, a new head unit would help
A head unit that does not have subwoofer pre-amp outputs of course wasn't designed with the intent of subwoofers, you'll get max impact with a head unit for this reason

Fourth, you MAY need to end up considering different wiring etc such as the gauge size, and a few other things, but none of which I can help you with until you tell me the prior

 

12gauge wires should be fine for the subwoofer wires.
8gauge wire for the powerand ground wire on the amplifier.

even tho the subwoofer box only has one input thats fine if the subs are not divided in the middle of the box, ya just run wires from one sub to the other.


so now you have to do some work of your own if you want these wired right.... now im asuming that those mtx subs SINGLE 4ohm voice coil models, now asuming like you said there is only one 2 wire speaker terminal on the box then your subwoofers are either wired at 2 ohms or 8ohms. BOTH not really set for your amplifier....

what you need to do then is take both subs out of the box, and on one side of the box you need to drill a hole large enough to fit your speaker wires thru for that one side that doesnt have the wire terminals, run some wires thru the hole and then use some silicone or epoxy or something around the hole with the wires so they are sealed.
then wire up EACH SUB to the one side of the amplifiers outputs setup on the BRIDGED labeled terminals. then each sub will be getting about 150watts.
ALSO be sure to use some RCA "Y" adaptors from your radios subwoofer output ran to the amplifier and Y ed off right before the amplifier so all 4 RCA inputs are used on the amplifier.
if your unsure what i mean, take a picture of the amplifier from both terminal sets and ill quickly edit the picture for ya....


it sounds to me like your system is just hooked up all wrong....

 

") Your head unit does not have a subwoofer RCA output, which although isn't a bad thing, they are not designed to carry only sub bass frequencies, therefore your subs are playing everything, and have no increase voltages on sub frequencies."

Well its a little late for that. Nobody told me,we ought to make a pinned topic on "subwoofer facts" and head units and such. I bought a new one from walmart. I could take it back...Now SHOULD I?
What head units DO have a sub only rca plug?

Its thumping a lot now and I kinda like to to put out "everything" it makes voices sound more real I think.

I bought a amp kit and it has 8 gauge power wire. I was really meaning from the amp to the subs.

I will look into the wiring. Thanks for the help.

 

There actually is a thread for subwoofer facts etc, I made it, yet for some reason, it has yet to be pinned
https://www.hondacivicforum.com/m_540822/tm.htm

Anyways, yes I do recommend taking it back
the box or model should say on it "pre-amp sub output"
or if it has 3 preamp outs, then 1 set is def for subs
they should def say somewhere on the box, just get a higher model pioneer HU

From the amp to the subs, 16 gauge will do fine
I still highly suggest checking everything else i suggested tho