Myvi 1.5 adv user here
Planning to get one underseat sub.

Current setup
Factory touch screen HU
Front speakers replaced with JBL CS762 2 way coaxial.
Rear door speaker: 6" stock

With this setup bass is too low at volume 15
I have no plan to change HU or addin amplifier. The current HU is capable of delivering 20W RMS X4

Can someone help to chose from below.
Kenwood KSC-SW11
PioneerTS-WX120A
DB drive euphoria EPS 8