I had same question not long ago. I wrote to Buchardt customer service if I can use for example 800W amplifier (Peachtree Class D) with my speakers (4 Ohms, recommended power 40-200W) and that was the answer:
You can use an amplifier with as many watt's as you wish, as long as you don't turn the volume up higher than the speakers can handle, it is not a problem at all :)
More wattage helps the speakers to perform better when pushing the volume up, so you cannot really get "too many" watts.