There's always socks, foam, etc. that you could stuff in the ports in a pinch. But I really don't think they'll overload, so long as you don't have them stuck in the corners.
That said, if you like the Spatials and liked the big Maggies on audition, no box speaker, however good, and the Harbeths are among the best, can do some things a planar/open baffle speaker. On the other hand, they can do some things better. You'll get a frisson from the 40.1's, but it won't necessarily be exactly the same as one from and 3.7i or a 20.7.