A friend came over with his Focals which were the oldef version of thes book self speaker (I think the only difference is newer models use beryllium tweeters).
These are rated to -3DB at 46 HZ.
They sounded great in my room.
Comparing them to my Revel Salons which are -3 DB at 26 HZ was not a problem at the low end.
They needed a sub for 2 channel listening and the missing octaves where obvious with bass heavy content.
If I had these Focals in a modest room, I would send a copy of the Pre-outs to a nice clean sub like the Martin Logan Grotto i using the crosses in the sub.
I would not cross my Revels or the Focals at 80 HZ. But that's me