Carefully plunge cut into the center section along the side so you cut through flush with the side. Grind the teeth off the bottom half of the blade and use that to cut flush with the sides and divider boards. Glue some strips of 1/2" stock to the inside of the chamber flush with the back of the baffle. Now just rotate the center section 90 deg and glue it back to the 1/2" strips. I believe the internal dimensions of each section is 11"x11", if so, this will work.
JVC RS-540, Sony UBP-X800, Onkyo TX-RZ730 (7.2.4), Onkyo M-5010, Elite Screens 100" 16:9 (Spandex AT DIY)
DIYSG 1099 LCR, Polk TSX-150C (DIY) Atmos, Yamaha NS333 Surround & Surround Back
Triple HS-24 mkiii sealed, Dual SAN 214.5 Devastators, Dual Crowson actuators, NU12000, NX6000, XLS-2502, MINIDSP 2X4