the db is the signal to noise ratio, the higher it is the better quality it will be, i would guess them to be 70-80, they might even tell u on the back, i think mine was made by phillips if i remember correctly, u could run an external amp through the high level inputs ive never used high level before so i couldt say what it sounds like, but putting in a better quality hu would be benefitial for the speakers to, (saying goes the system is only as good as the weakest point) yes there is a resistor in the tweeter housing,