Yea, you want to stay away from a peaky response completely! Or it will just be lame.
And the acoustics of the house is what makes the sound efficient so every subwoofer will be easier to sound good in a home then car. 100w is even surprising in a certain sized room.
About steady voltage, there are ALOT of common car audio amplifiers used in ca that keep the same output when your volts drop, it's called Regulated power supply...Competition amplifiers are the ones that increase or drop power to voltage. So i doubt thats it. Room acoustics is what is great.