I used black duct tape and an old camera bag strap (I shortened it) to keep my amp attached to my Zune in its DLO Action Jacket. The duct tape keeps the strap on the action jacket. Not the prettiest option, but it's cheap and very effective.
I use two thick and black rubber bands, one on each end, to strap my iHP-120 with my D10. Easy to un-strap, no sticky stuff. I also placed four very small silicone cones at the bottom, one on each corner, so that they don't scratch each other.