I do all my workouts on an 8" step, but had some concerns about blasts #1 and #7 with Imax 3. (I don't like the idea of jumping off the step at that height, and I thought those straddle jumping jacks in blast #7 were too tricky to do so quickly without one of these days catching my foot on the bench.) I don't want to lower the step for the whole workout because I don't feel like I'm working hard enough at 6", but I don't want to have to keep stopping mid-workout to raise and lower it for these 2 intervals.
My solution was to step down instead of jump off the bench in blast #1 (it's still a very challenging blast with the staddle taps, power 7's and jumping up on the bench). Also, I keep my High Step topper with one riser underneath it off to the side for blast #7. (It's the perfect size, since blast #7 doesn't require a whole lot of bench surface.) Blast #10 also has you jumping off the bench, but for some reason I don't feel as much impact jumping backwards off the bench as I do jumping off the side like in blast #1, so I don't feel the need to modify that one.
At any step height, this would be a killer workout. I sometimes find the off bench blasts to be the harder ones, so you could be using a 4" step and still get wiped out by any of the Imaxes.
Mephie