Do you have Reebok or Step Co?
This gets a bit confusing, because originally the Step Co step WAS the Reebok step. Then when Reebok changed to the black and gray step, Step Co starting putting their name on the step and calling it the "Original" step. So there are some steps out there that we recognize as "Step Co." but they say "Reebok" on them. You see this especially in health clubs that have had their benches for a long time. Then there are Reebok steps that are very different from Step Co and cannot use the same risers. The current Reebok steps are gray and black, and have just 2 risers that you attach in different places ( actually snapping to place ) depending on the step height you're looking for, with the options being 6", 8", or 10". Step Co. is a green and black bench that comes with 4 risers of various colors depnding on where and when you bought it ( gray, maroon, purple, or fuchia ). This is the step you see Cathe using on her videos. The options there for height are 4", 6", or 8" with the risers it comes with, with the added option of purchasing additional risers to raise it higher in increments of 2 inches per pair of risers. The risers don't actually "attach" to the bench. They stack under each end of the bench and are quite secure, but if you pick up te step to move it, the risers don't come along for the ride.
To my knowledge, there isn't any way to increase the current Reebok bench higher than 10 inches. At least, I've never heard of anyone with that particular step being able to get extra risers and do that. So if your "Reebok" is the original kind of Reebok step ( like Cathe's ), then the Step Co risers will work great and you just pile them up with the other risers you already have. If not, then you may want to check with Spri, because the person you spoke with may be confused and assuming you mean the Step Co. version. Then again, maybe you CAN increase the height of the current Reebok step, and I'm about to learn something new. That's always nice!
Good luck!
ErinF