With a test disc and a multimeter, you can find the clipped limits in total silence as long as you know the true power limits of an amplifier in advance. But if the specs are bogus, this doesn't work out. Or, the SMD or a handheld OScope can find clipping without audio.
This only establishes the maximum setting. To finish level setting and level matching, the system is going to have to play very loud somewhere.

David