RJ, a balanced connection has an inherent ability to cancel out interference impinging on it, but the more common shielded coaxial cable connection has no problem with interference in the vast majority of home environments, so there should be no difference in sound.
The material used for tweeter domes is just one factor in the sound quality. Any tweeter can be made to sound either dull or harsh through the design of the crossover network, regardless of how "soft" it is. Metal tweeters don't have to sound "metallic" and the Axioms don't.
