How many PRI/T1 cards can you install in a MICS 7.0 0x32 modular system? I have installed 3 PRI cards in a system, but I would like to add a 4th. When you look at the programming it looks like it should be able to take it. PRI-A, PRI-B, PRI-C, PRI-D is what is available. Has anyone installed a 4th one in?