Setting the speakers to small in a multichannel system and letting the sub handle the bass should give you the best sounding bass if the sub is of good quality. Even most tower speakers rated down into the 30+ Hz range cannot reproduce the bass as clean and effortlessly as a sub. Ideally, the xo should be 10-15 Hz higher that the weakest speakers' frequency response. I have a Klipsch RF 7 system with 10 in woofers, 250/1000 watts and I set all my speakers to small and MCACC set a xo of 100 Hz. The subs can't be localized if integrated into the system correctly and the system sounds good for movies and music. Subs can be moved around the room to get the best bass, the mains can't which is another reason to use bass management. Using the plus setting can lead to phase problems. makes null and peaks more pronouced and not result in better bass. It is hard to resist the urge to set tower speakers to large since we paid good money for full range speakers. This will also leave the avr with more overhead to do the midbass and Hi's. I brought my Elite avr for the power but I have learned the preamp and MCACC are just as valuable if not more for total system integration.
Klipsch RF 7 based HT 7.4, Pioneer SC 35, Acurus 200 Five, Dayton 18 Ultimxa Dual Sub Cab(2), Dayton 18 Ultimax Large Vented Sub Cab (2), on Berhinger I Nuke DPS amps, Samsung BDP F 7500, Asus/My Book Live HPC 4 TB
Yaquin VK 2100 amp, McIntosh XR 5 speakers, Samsung BDP F 7500