Can a power amp have too much power, risking damage to a speaker?

Yes, but the speakers will hurt you before you can hurt them.

"we often get out an audiometer to ensure the sound-pressure-level is well under 95dBA for sustained periods."

This would be less than ONE WATT fed to your Klipsch speakers. I think you’re good.

A little historical context:

When Bose 901s were first introduced to the audio world, they had a power rating of 270 watts (If memory serves correctly). They were having incidences of catastrophic driver failure. A quick study revealed that little Pioneer receivers (around 10 WPC true RMS power) were the culprit. These little boxes were, essentially, turning into low amperage DC power supplies at sustained clipping for long periods of time (hours). Bose raised the "recommended" minimum amp power rating to 50 WPC. Problem solved.

Doing some quick math here, your Mac and K'horns or LaScalas should hit peaks of over 130 decibels in your room. Should be plenty of dynamic range available on demand.