There are no subs, just a woofer. It's possible, even likely, that the cabinet is not tuned to the woofer. I don't know what herald muscle magnets means. If the woofers and mids are decent, then it might be worth tuning the cabinet using some speaker design software, and then replacing the tweeter with a proper dome, and designing a new crossover around them. Don't buy a commercially-made crossover, they're designed for ideal drivers (i.e. constant impedance across entire frequency range) that doesn't exist.