buzzin sound is usually bcz of interferance of electirc wires on speaker wires or pres
well if u dont have a 2.1 option in ur amp, which i think wont be there, than i think u can set differant gain or crossover for ur new speakers and woofer.
if getting loud sound in not ur primary concern, u can connect ur speakers to the deck and set the crossover on it ( most new pre have this option ).
in sum it's like that tht exploding or something voice is total disturb and bass is at it's height
the speaker is excursing more then its maximum limit, its overshooting its Xmax. any other configuration resulting in less power in base region would solve this problem