any speakers will sound better when driven by an amp. an added benefit to using sn amp is that you can set the crossover to block out the really low sub bass. this will allow the speaker to play cleaner, louder (i know, you dont like loud), and more accurate. with all the power delivered to the correct frequencies.
but as i said earlier, they dx7's are so efficient that they will even sound great off the headunit. if you have an amp, then you should use the amp.