The question is whether one wants "completely adequate" or prefers something "good." An audiophile would dislike any of the Smart offerings. People who just like to listen to music while they drive would probably enjoy it in any configuration.
I'm no audiophile but I have an aftermarket HD radio, replacement speakers, and have sound/vibration dampening internally on the door skins to abate outside noise and enhance inside sound. No subwoofer needed for good sound in my setup, but then I feel wicked-loud music in a car is nonsense.