Asterisk for Call Center

I’m trying to implement a telephone exchange for Contact Center which need 8 lines, 6 are to receive and make calls from the softphone there each PC, the other 2 will be designed to Fax and Posnet

We have an IP Telephony system provided by the company Telmex. So far I researched and manages give that I do not need any Digium board since the lines will give me the Telmex, which remains for me is to configure the SIP extensions for each user, and install on the jobs the softphone, it to me this is complicating the issue of the configuration of the FAX and Posnet. In addition to some schedule lines must be closed and calls must be routed to an answering that too is something I have yet, my local network is formed by a CISCO Router RV082.