Universal truth .... :clapping: (in more than just audio too).
I agree that the 12" driver will go down in the LF but quality and integrity is essential. Good implementation is needed. Getting a good three way is the way to go but its also very expensive. A nice sub woofer will also add some weight to the sound but integration is critical.
My opinion though is that a lot of deep bass rumbles are ultimately not real (especially in movies). For example, I have been around a few car crashes in which the sound was actually nothing near anything our movies show. There are definitely no warp speed sound waves blowing up glass windows etc aka Transformers. Same goes for the bass drum in a rock concert. A driver that goes down to 60Hz is plenty. Most natural sounds are well within the capabilities of 6.5" mid woofer.
Another problem is that sometimes too much bass will eat into your mid range robbing some of the sound. This is a matter of taste.