PE4 will (should) work in any PCI slot
PE1 will require a firmware upgrade from Active Silicon if being used in Slot 2 (bottom) on a 4,1 or 5,1 MacPro
Contact: phoenix.support@activesilicon.com
for reference:
Slot 4 (top)
Slot 3 (mid)
Slot 2 (bot)
Slot 1 - Graphics Card
S