Have above system now 1 yr old. Have what appears to be 2 cards that process 2 lines each. Am told I must remove the 4 line CARD and replace it with an 8 line CARD. Looks like I can add 1 more 2 line card to get the 6 lines I need. The box has several additional slots for same type cards as the 2 I have. They refer to card in the singular as if I will remove and replace a single slot. I think I'm being sold more than I need. Any thoughts?