Hey Matt,
You likely mentioned this, but why are you having bass issues with a rear ported speaker? IME, it can be quite a useful tool, in that the closer to the front wall, the more low bass energy you have, to a point. Rear ported speakers can get muddy sounding bass if too close to the front wall. Maybe this is your issue?
Are you locked into a speaker position? Seems as though you have some freedom. Your room is just a bit smaller than mine. Mine is 17 1/2ft X 22 1/2ft X 10ft high, and I have had no issues with rear ported speakers here. I just pull them out into the room until I get the right balance of punch and low end, then tune the room accordingly to make it all balanced. Given your room size, I think the 60hz area is likely your biggest problem. Missing some slam? The traps likely helped this allot, but you might need more trapping.
Bass is the number one issue with getting a system to sound right though, so I can understand your frustration.
One thing that I would do in that room, where that drop ceiling/soffit area behind your listening chair is... I would deface the front of it and stuff that with all the insulation I could get in there, then cover the face with a big speaker grill of sorts. This will go a long way into balancing that room more.