Plugging the ports on the Primus 250s did not work, or rather it worked too well. Instead of attenuating the bass, it eliminated it.
I realized last night that they sound good with most material most of the time. It is only on unusually bass-heavy passages that they become boomy, and I can live with that as a tradeoff for their many positive qualities. (Besides, this boominess is clerly a property of the room, not the speakers, since it occurs with all floorstanders.)
If I do decide to get new speakers at some point (by no means a certainty), then I might look for the smallest high-quality floorstanders I can find. (Totems are no longer an option because they stopped shipping them, and there have never been local dealers.)
The PMCs look nice,by the way, but Oklahoma is not even on their distribution map!