I don't believe the underseat speakers are actually subwoofers, just normal woofers. The crossover in the basic speaker setup is integral to the head unit so I'm not convinced it's possible but could be wrong
The HK setup is completely different and takes a digital feed from the head unit into a DAC amplifier and then filters the frequencies to the various speakers and subwoofers.
The HK setup is completely different and takes a digital feed from the head unit into a DAC amplifier and then filters the frequencies to the various speakers and subwoofers.