I have six sealed 12" subs powered by an EP4000 and I only use Dirac for the boosting. It can boost up to 10dB so as long as you place your subs wisely there is no issue at all to only use the boost provided by Dirac. I run three of my subs nearfield and three in the front and I can play to 7Hz so that the couch shakes like crazy. So I'd say it can boost enough no issues.
I see a lot of people building very small sealed cabinets and what happens there is that you get a much sharper roll off with peaky mid bass. For an 18" driver I'd not build a box smaller than 200 liters. With the correct box you don't need to boost that much and it has a lot of other benefits as well like overall sound quality, less compression and heat etc.
Room| Treated | Sound| Front: Ino Audio i32s, Center: Ino Audio i16s, Surrounds: 6 x Ino a2, 6 x Ino a1, Subs: 6 x Ino Infra-Y|
Picture | Epson TW9300, Seymour Center Stage UF 130.4" retractable 2.35:1 |
Electronics | Arcam AVR390(Dirac Live), 3x Ncore nc400 monoblocks, Emotiva XPA-2 Gen2, EP4000, Panasonic UB700, Allo Katana + Isolator 1.2(Roon bridge/DAC), ATV 4K |