I am assuming you are going to PRI? The new DTI card should go on the right hand slot. The spare CID should go on the left hand side slot. Your fiber card should be just fine where it is. Just a NOTE: If you are going to PRI you will need a PRI enabler keycode, and also you will need a combo card next to that 2 port fiber card. The PRI enabler keycode lets you program the system for PRI, and the combo card is what keeps the timing. Without them you would be SOL.