Thanks for the replies.
I had connected to both terminals because that was the recommendation in the manual when using the line-level inputs. I just finished calibrating the speakers and was happy to see the sub performing as well as it did with the previous receiver (as far as the sound meter and calibration tests are concerned).
I'll go into one terminal and observe how that sounds.
My assumption is I'm still better off with my PSB active sub than the bundled passive sub. It hasn't even been unboxed.