Stereo & Electronics - Monsoon not giving good bass signal to amp

I got 2 jl audio 12-w3 d6's on a class d amp. I wired the setup in my camaro with a dual 12'' box and this setup POUNDS ridiculously loud, it got the signal from rca through an aftermarket hu.

I wired the setup to my trans am that has stock monsoon system through speaker level inputs and I am just not getting any bass. If i crank bass boost up on the amp it thumps a little bit but I am not getting the right setup. What is the cheapest way to get this setup working? My amp takes speaker level inputs as well as rca.

Line-level adapters are usually better....

With that kind of a setup though - you have to be looking at aftermarket HUs.

did you hook it up to the correct wires?