The "Black Box" PSU is a bit beefier than it's blue sister, powering up to four (4) PA-FOUR Plus units or twelve (12) PEQ2R's. If you started with a Blue Box and added a ton more channels, you'll want this. The "Black Box" is also available as an option for the PA-Four Plus and PEQ2R on our site...y'know, because we care!