Loud Snap at High Volume

Don't know where the ribbons are crossed over.  This is my first experience with ribbon tweeters.  Love the sound of them, but maybe they can't be pushed.  Discouraging.

It may be you are overdrivign the woofers.  Try plugging the ports on the rear and see if the problem vanishes.  Not saying you should run all the time like this, but it is possible severe low frequency signal could cause excess excursion below the port frequency.

@erik_squires    Erik has got the answer. The dynamic range of classical music can be huge. Play Fanfare for the Common Man with cannons and turn the volume down until you don't hear any distortion. That will be your approximate system limit. If you want to play loud and not damage loudspeakers you might want to look at loudspeakers that can do that with ease, like big horn systems. 

The Borrensen web site says the tweeter crosses over at 2.5KHz.  That seems too high for the tweeter to generate a whiplash sound by itself.  However, my first guess goes with what Erik says -- a woofer bottoming out. That can make a cracking sound, particularly if the recording contains subsonic material. I heard one recording the other day where the musicians were on a wood platform. Everything sounded fine on my second system (no sub) but you could hear them stomping here and there on the main system with a subwoofer.  The sub didn't bottom out, but the noise wasn't very musical. 

If you have access to DSP or tone controls, it'd be interesting to see if the problem continues if youi back off a bit on the bass, or can cut the response below 30 or 40 Hz.

@erik_squires  Thanks for the suggestion.  I will try that although the snap comes at high peaks not low.  Should have mentioned that.