I am pretty positive that the mounting plate that you have there is specifically a Panamorph AK7 Attachment Plate. You would certainly have a VERY solid installation with that paricular plate and Chief mount that's for sure!
How is your sub sitting on the floor as in "is it coupled to the floor"? Is it on carpet, hard floor? Is it on regular feet or spikes?
What I am thinking is how you might be able to isolate your sub from transmitting the structural vibration! For a possible commercially available solution you might try placing the sub on a Auralex Gramma sound isolation platform if your particular sub will fit on it OR you could try putting together a similar Do It Yourself solution! The Gramma is nothing more than a carpet covered wood platform with some type of dense foam blocks as feet.
Some people swear by the Gramma for subwoofer sound improvement, as they say it tightens up the subs sound but maybe it could help with your structural vibration transmission issue!
Try to "decouple" that puppy from the structure!
The Gramma manufacturer can be seen here:
You can see the detail of the Regular Gramma underside foam construction and purchase here :
You can see the detail of the Great Gramma underside foam construction and purchase here :
Also, your pincushion is really not that bad... Nothing a little overscan can't handle!
...Glenn Edited by Glenn Baumann - 4/26/13 at 11:38am