UPDATE: I think I know why the RX-A5 didn't have as much bass. The surrounds on the active woofers are too stiff. They barely even move when touched. They are made of resin-coated cloth, and I think that resin has dried out and become stiff. I have seen that happen on other models too. So I recommend replacing those surrounds with new foam ones, which will be much softer and flexible, producing better bass.
Music: "Object of my Desire" by Starpoint (1985).