Joseph,
I have seen some setups that use the 534’s as rear surround. I think you will be fine with your setup. You may want to play a bit with the placement and maybe push them a bit in back somewhat closer to the rear surround.
I do think that even at an angle mounted parallel to your listening area they will sound good. The Bi/Di switching can give some great sound effects. I switch between the settings to achieve different sounds.
You may want to experiment with placement before mounting permanently. I now have the 534’s mounted with the bottom of the speaker 54 inches from the floor where previously they were about 40 inches from the floor.
Jack