I have 3 HSU CCB-8s across the Fronts in our Atmos System in the Games Room, and frankly they are fabulous. They are the best center I've ever heard. If I were you I'd bring them in and test them out using your sm55 bookshelves for the surrounds.
If you are not completely satisfied with your purchase, you have 30 days from receiving the item to begin the return process.
I brought mine in from California to Vancouver, BC and have been happy with the purchase for years.