Bozzy,
Don't worry about "overpowering" your speakers - you're more
likely to cause damage by "underpowering" them.
The rating on the speaker is how much power they can dissipate.
The power rating on the amp is how much it can put out cleanly.
However, you don't have to use all the power of a high power
amp. If it takes 25 watts to power your speakers to a given
sound pressure level - it doesn't matter to the speakers
whether that power is being delivered by a 50 watt amp or
a 500 watt amp.
However, for the amp - it is better to have more headroom -
power above that required.
If you have to transport a heavy weight up the stairs - who
do you want to do it - a child who can lift the weight - but
just barely - or a guy who works as a piano mover?
The more powerful amp can deliver the power more cleanly -
with less distortion on peaks - than can the lesser powered
amp.
For a given sound level, you are not dissipating any more
power in your speakers, just because the amp is more powerful.
Dr. Gregory Greenman
Physicist