I would prefer to slightly underpower speakers than overpower themIf you mean, operate the speakers slightly below their spec'd limits (~100W?) -- agreed.
If, OTOH, you mean not having enough amplification power to meet these spec'd limits -- don't do it! Clipping can damage the drive units!
The idea being that, even if the amplifier's energy output exceeds the speakers', one probably won't play loud enough to reach thermal limits; with an underpowered amp, you can easily hit clipping!