Just two other points. Those long slot vents have to go round corners. They are not straight.
You can still EQ with the Bash amp. Get yourself an equalizer to go between the LFE out and the Bash. However 28 Hz is VERY low, and it will only be 6 db down at 22 Hz. Depending on your room that could even be a good thing. I would see how it sounds first before adding Eq, chances are you won't need it.