if you want to retain the factory speakers, here's how you can improve the midbass
1) If you are using a generic android panel, you might want to look into something like the new onkyo android panels that use pioneers hardware/software or nakamichi. They have better in-build signal processors and amplification which means cleaner signals to your speakers. Better EQ software also results in better output
2) Try Sound deadening your front doors and rear parcel shelf. In this case, doing the rear doors isn't a must since you dont have any speakers there. Deadening the front doors basically eliminates the metal resonance which negatively impacts the midbass. Also the plastic weather sheeting on the inner panel flexes. Deadening both the inner and outer metal layers creates kind of a sealed environment for the speaker. This drastically changes the way the speaker is gonna sound. You'll feel the mid-bass being a lot more punchier
3) Adding a small amp under the seat is a good way to give clean power to your factory speakers since the generic android panels are really pathetic when it comes to clean signals. You don't need a lot of power for these speakers. However, small footprint amps aint always cheap. That being said, pioneer does make a small D-class amp. The cheaper option to the would be a soundmagus mini amp. If this is an option, we can discuss that in detail then
4) The final option is to add a active underseat sub. If you just want that low end punch at low-normal listening volumes, Nakamichi has a nice little 6x8 underseat sub which will do just fine. You can always opt for their 8 or 10" under seat subs too but from what I understand, the 6x8 will do just fine in your case
