You should plan on one ballast per 4Bank fixture, not one ballast for all four fixtures. A 4Bank fixture uses a ballast channel arrangement intended for that single bank, so four 4Bank heads would require four ballast units total. You would also need a separate head cable to connect each fixture to its ballast. In short: for four 4Bank fixtures, expect to need four compatible ballasts and four connecting cables. Check the exact Kino Flo fixture/ballast compatibility chart before buying, but based on the setup described, one Mega 4Bank ballast would not run four separate 4Bank fixtures.