Bass is one thing the HK system does not lack! I know guys talk about not liking HK in chargers but sounds like you have a Challenger.
Pop the trunk and lift the floor lid up, you should see two subs there. If they are there, well there might be some other problem.
I’m not an audiophile or anything but I like the HK in my Challenger, one of the things I really like about it. My HK in my BMW sucks.