Hi Ali,
Don't confuse the number of shots in the bracket group with the delta EV for each of those shots. The 1D3 and 1Ds3 and take 2, 3, 5, or 7 shots in a bracket, and the maximum delta EV is 3 stops either side of the mid-point (that's total, not 3EV between each and every shot).
I'm not sure on what all of the other models allow, but typically they only allow a delta EV of +/- 2 stops, and often only a 3 shot bracket.
If you need anything outside of that then you need to "go manual".