Since when does underpowering a sub hurt it? Ask Audioholic. "No speaker, in the history of speakers, has ever been blown by too little power. Ever. I don't care what your friend told you, he's a dirty liar." That's a quote from his signature and it's completely true. The only way possible to damage a sub by "underpowering" it is to attempt to feed it more power than the amp has, causing the amp to clip. This will feed the sub a square wave rather than a sine wave. The square wave will cause the voice coil(s) to overheat. That could potentially harm it. As long as you know what your amp is capable of and you know how to properly set the gain, you're not going to f*ck sh*t up by underpowering it.