Adding booster fans to your ceiling A/C vents.

Keep in mind, that blower is 123 cfm. The A/C puts out 320 cfm total, so you are pulling over 1/3 of the capacity through that single vent. It will work, though 3 blowers would create a negative pressure in the ductwork, pulling 369 cfm while the air was putting in 320.
With one or 2 of these, you will virtually eliminate the flow from the other vents- In effect, you are robbing Peter to pay Paul.