Dastro
What a difference that box made.
It’s a great design, and was far ahead of its time allowing for full range, and in rooms that do not support it.
You are basically turning the 801 matrix’ massive woofer box into an EQ’ed subwoofer with one setting ...a factory designed one ..... settings on the BAF being different for each particular 800 - 805 matrix model.
The additional and maybe even greater benefit imo, is that the EQ boost allows the ohms requirement to remain in the 6 ohms range on 100 hz and less ..... not as taxing on an amplifier.