Hang on. The issue is whether or not the 805 sound good with rear boundary support. They are NOT voiced for that big upper-bass bump that will result. I tried several manufacturers' supposed "surround" speakers that seemed to be just reconfigured versions of their 2-way monitors (JM Labs, PSB, et al), and was surprised at how congested they became as I pushed them back against the wall. This 2pi/4pi correction stuff is a critical criterion in speaker design.
I settled on the Boston VR-MX surrounds because they simply sounded great up on the wall...even full range, and they look terrific too.
Crossing at 80Hz may not be high enough to eliminate the effects boundary reinforcement will provide for the 805. You may have to cross higher. Good luck.