Just my two cents...I completly agree.
I used to work at a sound audio shop in my area. they said the number one thing that people dont understand is that more times then none, underpowering a speaker can damage it worse then over powering it. When you under power the speaker you get so much distortion that it can ruin the coils in the speaker over time.
Your amp is trying to take a low whisper and turn it into a scream. Another example... trying to take a 1M pixel picture and blow it up the size of your wall. This is wear the distortion starts filling in the spaces.
As far as the power rating on amps. I used to sell them a few years ago, at that time they didnt have any base line for testing results. Some companies like sony would put 16V's to an amp and see how much power it would get in half a second. Then they would use that as their rating. Company's like alpine would under rate their equipment so that their amps would sound better then all the others in that product level. I heard of rumors that they were trying to get restrictions on how they rated amps but I dont know if it happend or not.
if you dont want to get into the nitty gritty, try to get the same amp and sub manufacterure because they are tuned together.