s&r - no, I am correct (and not "partially"). An underpowered amp is more likely to damage speakers than is an overpowered one. Both require the same caveat: keep the bleepin' volume down.

Repeat, a 40W speaker is properly matched to an 80W "valve" amp or a 160W solid state one. This is a rule set by stereo users and is not found in any book I know.

Not all solid state amps want to see a lower load than the "nominal" load at which the amp is rated. A 50W amp is rather small, by modern standards, and will have only one pair of output devices. Higher powered amps, say 150-400W, will have 5 to 10 pair of output devices with a concominant lowering of the output impedance and a more efficient energy transfer into lower impedance loads. Huge amps often deliver the most power (and obviously the most amperes) into loads of less than 1 ohm.

Although the convention is to rate amps into 8 ohms for home stereos, many (if not most) design them for a compromise value of 6 ohns. Many speaker makers also fudge a bit here and make a speakers whose crossover frequencies are correct for 6 ohms also. So in reality you probably have a perfect match at 6 ohms each, but there is no way to prove it!

Answer? What you have is perfectly fine, just do not turn the volume up past the point at which the music sounds clear and clean. End of problem.