I just bought JL Audio's Stealthbox for my 93 325i (bmw). This is exactly from JL's website,
"The Hard Data:
Contains two 8IB4 subwoofers in a semi-enclosed infinite baffle setup. 150 Watt power handling. Can be wired for 8 ohm stereo or 4 ohm mono. "
So I need an amp to power just the...