even if it can play bass, you still have the whole factory EQ curve built in. Factory head units have sh*t speakers, they use heavy EQ boosts and cuts to make up for it. You wont see it because its invisible. However now you use aftermarket speakers that was meant to be put on a flat signal but no, its subjected to the factory EQ boosts and now you amplified it. What happens when there's a lot of EQ boost and a lot of amplification? Clipping and distortion. also your new speakers will most likely not like the factory built in EQ curve.
This is exactly what i meant by if you have garbage and amplify it, you'll only get louder garbage. it might sound okay to you but you need to remember, people have different ears. Others might throw up after hearing the same system.
I literally cant stress enough on the importance of a good high resolution quality signal with actual audio controls such as EQ, time alignment and crossovers with a quality 24 bit or higher dac. Literally makes or breaks your setup.