Have you measured the loudspeaker outside (i.e. without room boundaries)and then in room with a calibrated mic and REW for starters? They might be tuned high as your post suggests, but you won't know until you measure and the room below 300 Hz can have as much of an effect on the response.
You can post this in the Lab/Enclosure section
Personally I would be happy with sealing the ports, and adding multiple subs along with measurements for the best in room response period.
Best,
Anand.
