I could not watch the video.
It is most likely that the woofer needs to be replaced or rebuilt, It's not impossible that the internal amp is the problem so remove the woofer from the cabinet and play it directly from the receiver front output after setting them to large with no sub so bass will come from those speaker outputs. Be careful not to play it too loud at first.
If you are in the US I recommend you contact Millersound. They rebuild woofers and do great work at a fair price..