I am learning phone systems now and have a system I use at home for learning. It is a used dxp plus.I have a dst16 card and an ist 16 card in it along with srv card and cpu card. I also have a ring generator. Anyway, I would like to hook up this phone system to my regular analog phone line I have at my house for calling to the outside and receiving calls from the outside. I believe that I need a dxast-8 or a dxpco-lp4. I am not sure. Please let me know which. Also, let me know if anyone has one for sale or a place to buy. thx!