I agree with the use of a REL sub. The above problems with subs have not been an issue with REL because there is a specific set up procedure involving placement where the sub works with the room instead of against it.
Also, REL subs are tunable within 2 Hz. increments from 14 Hz and up. Most room nodes in the room your size are dealing with 50 to 60 Hz. and their overtones which is well above the REL's crossover point.
Also, REL subs are tunable within 2 Hz. increments from 14 Hz and up. Most room nodes in the room your size are dealing with 50 to 60 Hz. and their overtones which is well above the REL's crossover point.