Will high SPL subwoofers damage planar speakers?

As far as the sub damaging the panels I doubt it. Many people have had Quads paired with subs before. Hopefully they can chime in.

"Quad's on the other hand will go into protection mode if played over about 95db."

The protection circuit is not saving Quads from damage.

sorry I beg to differ no electrostatic goes as loud as a dynamic speaker, the issue is the amount of air displacement and throw that the diaphram can move before it hits the stators.

The innersound are okay speakers at best, I have heard them on several instances didn't blow me away at the least.

At shows I heard a set of Vivid rattle out the lighting cans out of the ceiling, never heard an electrostat that could move enough air without getting hard at loud levels and compressing.

There is no perfect speaker. Some speakers excel at rattling light cans from the ceiling and other speakers excel at nuance and truth of timbre. They all have their place and everyone has different taste.

Agree 100% w Rrog's comments. My 989s went into protection mode everytime I play orchestral pieces with cymbals eg. Rach II 3rd mvt. Whether your run a crossover to move the bass to a sub is irrelevant. Want to play loud? get Wilsons.