My old Fujitsu that was originally in my van hooked up to that Fujitsu equalizer made the headlights dim worse than my new stereo system I got now. It also had its own sub under the dash. I ended up hooking that to one of those $20 Roadmaster bass tubes from Wal-Mart. It sounded alright. I was stuck with radio though. The tape player didn't work. So I ended up soldering some RCA cables to the cassette's line-in circuit after trying to find it. Then I hooked my RCA Lyra to that and was only able to enjoy 1 or 2 CD's worth of music.
My amp does 160W/channel with 320W/channel of peak power. So that would be 320 total RMS and 640 total peak to run both woofers in my subwoofer. I have to be really cranking that son of a bitch 'til my ears just start to bleed to even notice any dimming. So having said that, I'm willing to believe that underpowered amps can actually draw more power than amps that have plenty of power. I made sure I can get the most powerful amp I could afford. I got the gain on mine about 1/4 of the way and it sounds pretty damn good. I'm still tweaking here and there to get it just right. Also remember that an underpowered amp can damage your sub. So it doesn't hurt to try to get more power than you need, or at least meet its power requirements.