Looking at your speakers, nice speakers btw, I wonder if those vibrations aren't caused more be the two corner ports that fire towards the rear? Because if your speakers were vibrating enough to make the cables vibrate you would have larger problems than damping your speaker cables. At least I would think so.
Vibrating speaker cables
By coincidence I happened onto a major factor in improving bass performance and speaker transparency: vibrations in the speaker cable generated by the speaker itself! I run Duevel Bella Lunas supported by Symposium Svelteshelfs in turn supported by Final Darumas on carpet flooring over wooden floors, into Bybee Golden Goddess Speaker Bullets into Auditorium23 cables. Having by accident noted speaker generated vibrations in the cable, I used Black Ravioli Pads to dampen the cables as near as possible to the speakers’ binding posts and: Kazooks! major tightening in bass performance and depth as well as overall transparency. While this all sounds a bit outlandish, I suggest trying it: the results in my case were nothing short of spectacular.