what is the weakest link in my audio chain

Benqsun: I don't see any weak links in your system. If your really want an upgrade to have a noticeable improvement look to your main speakers. But the Paradigms are nice speakers and if you like their sound you would be hardpressed to do better. I would spend more time defining precisely what it is that you find lacking before I started picking an item to upgrade. The items I would not even consider changing are the last three you listed. "Upgrading" those items is not upgrading.