Granted you dont want the amp at 100% output all the time because it shortens the life, but underpowering will never do any harm to a speaker. Overpowering will overheat them and can fuse the coils causing them to distort and make cool cracking noises. If you run yours like mine, which is at 120 db constant cruising, then you want a little extra wattage to keep the amp nice and cool. Your not competing theres nothing to worry about. You could run it on your amp now, but your amp would get hot.
Also most AMP ratings are done when the amp is cold, fresh and at 1 frequency such as 1khz. Or whereever it performs best usually with a high distorion ratio.
My MTX amp claims to be 250 watts. Electrical testing proves it to be about 35 RMS.
Sub Watt ratings are another story and not needed for this thread.
call BDR50h, have him hook you up with a amp to made to match that sub and be done with it. Seeing that your intentions are to just have a little extra kick, None of this other bullshit is neccesary.