bruh - i guess just keep this in mind as i speak from personal experience with acros b/c they are completely in their own class in terms of light/par. if you keep with the "add more prime" route, which is certainly viable, you probably will need 4+ to get to a "base line" par level for acros (your 40B is basically 2 of 90 reefer's 20G cube). but even 4 isn't gonna be enough for "all acros". I'd guess with 4 you'd get to 200 - 300 par, which would be good for beginner acros like green slimers. however, some of the more higher end acros that show more of the crazy pink/purple/blue flourescence will need par levels north of 500.
i guess what i'm trying to say is, with the "add 1 more prime" route - you will probably be fine for 70-85% of all coral choices that includes all softies, lps, and SPS (all non acro + maybe 25% of all acros). However, that remaining % of acros which inclues most of the higher end, the most coveted and prettiest acros, a "prime only" route you'll need like 6 - 8 of them. at which point you'll need to also think about the amount of wires, mounting racks/arms, and available power strip, to see if it's practical or if a higher end/stronger light may be a better choices.