How to wire a powerful amp with two speakers to avoid damage

Paul (& Angela) the amp would barely be working hard at all & probably wouldn't get much warmer than it runs at idle dissipation. You can in fact operate very high powered amps into low-wattage speakers without doing any harm at all, provided that you exercise reasonable restraint. We once drove some 100-watt-rated B&W speakers with a Mac2500 amp (500 w/ch. conservative) with no problems. In fact since the Mac never went into clipping, we were able to drive the B&W's at about 300 watts before they were audibly straining to handle that amount of power. At any higher power level we would have gotten in trouble burning up a voice coil, but as long as you're even reasonably careful then there is no problem in doing this.

Sean is correct. More speakers get damaged from underpowered amps than from overpowered ones. The amount of power delivered to the speakers is dependant upon the voltage delivered to the speaker, which is dependant upon the volume control. If you play the speakers at a comfortable level the big amp will not harm them in any way.

The heat generated by an amp is mostly caused by the current in the output stage. In a pure 'Class A' design the output current is at a very high level all the time and thus the amp is hot all the time. In a 'Class AB' design the output current is at a low level unless a lot of current is being delivered to the load. Under low listening levels or with very efficient speakers the output current is small and the heat being generated is also small.
Chris

I have never had a problem running a very efficient speaker with high wattage as long as the volume is kept low to be certain it does not clip! (as mentioned above)

Thanks, Chris and Bob. Good knowledge to tuck away. AJ

Just one more tidbit: why do underpowered amps potentially damage speakers? The reason, as previous posters pointed out, is that they are more likely to go into clipping in the listener's quest for louder sound. Nearly all of the power in a music signal is in the bass and low midrange. When the signal is clipped, this distortion generates an abnormally high proportion of power at high frequencies. So even though the total signal power can't increase (the amp is clipping because it's reached maximum output power), more and more of the power is appearing in the high end of the frequency spectrum. That's part of why it sounds so bad. Plus, it's this abnormally high power in the upper midrange and treble pouring into the tweeter that burns it out. The voice coil in the tweeter is sized for "normal" amounts of power in the treble range. Clipping causes abnormally high levels of power in the treble range, overheating the tweeter voice coil and causing it to fail. Next to go is the midrange speaker's voice coil. It's beefier than the tweeter, but still relatively wimpy compared to a woofer voice coil.

Bottom line: I agree with previous posters and would not worry about hooking up 75 W amps to speakers with a labeled rating of 25 W. I would be cautious, though, and start with the volume turned ALL the way down, and cautiously raise it, listening to see how the speakers react. At the first hint of distortion, back the volume down IMMEDIATELY.