Too powerful of an amp!?

Just don't trade quality for power, which often happens.  Most of the time, even with your less sensitive speakers, you'll be listening under 25 wpc--maybe even under 5 wpc.  I'd recommend spending your money to get the best amp you can get and if you have to pay more for a 500 wpc amp, you'd be better off getting a higher quality 100 wpc amp for the same money.

Jery

Great advice above.  We are all reconciling the following truisms: 

1. Never under power loudspeakers if you can avoid it.  Too little power can damage speakers. 
2. When buying amps, don't forget when you buy a 400W mono block, or the like, that it's the first few watts that matter. 

When an amplifier clips, nasty stuff typically happens to what the loudspeaker gets fed and pushes back.  

When we listen, even at loud volumes, the first 1-8 watts are most of what we use and hear.  A 9 watt tube guitar amplifier will blow you out of the room, compared to these massive wattage amps we see today.  

Sorry, don't mean to confuse you.  It's all good advice above. It's a delicate balance.  Going over with a good quality amp is usually a good thing!

@jbhiller 's advice above struck me wrong until I kept reading.  You won't damage an amp with a low power signal unless it is clipping/distorting.  So buying a low power amp AND turning it up too loud will damage speakers.

Jerry

True @carlsbad2 !  

So very true.  I powered KEF LS50s with a 300B amp! (8 watts)

If you don't listen loud, a low powered amp won't be harmful. The other consideration with a low powered amp is lack of headroom.

All great advice.  An important aspect of matching amps and speakers is synergy.  The watts alone won’t tell the full story on how they’ll pair together.  Another poster brought up Horse Power under the hood which is a good comparison, it’s not just HP though, it’s Torque, it’s how a car is geared and various other factors, it’s when the engine in a car has synergy with the rest of the car that true magic happens.  Same with speakers and amps.  Research what mates well with your speakers, Tube or SS, do they need headroom to really shine?  Are the speakers on the brighter side?  Pairing Tubes or Class or SS amps known for warmth like Macs, Pass, Krell, Parasound, Cod to name a few.  Your speakers will likely do very well with amps that have some headroom, provide stability.  If you like Mac’s, a great place to start with their power / autoformer technology.  Good Luck, enjoy the journey!