When I first installed my 4 in-ceiling speakers for atmos I did not have back boxes installed, I have Bowers & Wilkins CCM682's. I eventually made back boxes identical to the B&W back box specs and it made a huge difference. If your speakers require them I would definitely get them if they do not require them I would not worry about it. As op said some in-ceiling speakers do not require them. Also keep in mind that a backbox also protects the speaker from dust and anything else that may be in your ceiling. I liver in a condo so water pipes and electrical are the ceiling.