They're tough but beautiful. I've had mine with a maroon for quite sometime w/o problems . In fact sometimes the maroon darts at him when he goes into his guarded territory. Be sure the PB has lots of space, is well fed(greens) and try not to add new fish to the tank. If so, do it after a feeding and after the lights have been off for at least one hour. You also may have to rearrange rocks to re-establish territory and feed in two different locations because the PB can get especially aggressive during feedings.
Hope your marron recovers. Is he a yellow strp or white. I've found the white to be a bit more aggressive than the yellow and as result may be better suited to hold his own with the PB. Good luck