How to connect Adtran T200's to Asterisk?


I friends office currently runs a a system where they have 2 Adtran T200 HDSL2’s connected (via what appears to be a RJ45 cable) to some sort of box (I think a pbx system box) which then connects to a lot of logic boards(via cable that looks sort of like a wide serial cable) . Which connects to a server which can handle 40 calls.

I am discussing with him about upgrading to asterisk.

He doubts his bosses would want to switch to a completely SIP based system, so what would the best way to connect the Adtran’s to the Asterisk box?