Having owned the C1 and now the C1 Signature I have never heard of that problem. Does it happen with both speakers? Does it happen only at high listening levels? I've driven mine with a Bryston B100 and now an Octave V70Se. I've heard C1's with Naim - Sim Audio and Burmester. Since the speakers are passive I would think it is something upstream. Try without the conditioner. Any possibility of borrowing a different amp? Another option may be to bring the speakers to a friend or dealer and listen to the same passages but on a different system.
That being said I have overdriven mine to where the woofers bottomed out. But that sounded more like someone hitting the cabinet with a padded baseball bat. But it didn't ring or last past the low note.
That being said I have overdriven mine to where the woofers bottomed out. But that sounded more like someone hitting the cabinet with a padded baseball bat. But it didn't ring or last past the low note.