The easiest thing to do here would be to monitor the PBX interface itself for errors. Inserting another piece of gear gives you another potential point of failure in series, or for temporary troubleshooting use test equipment such as a T-BERD.
If this isn't feasible, the best Adtran box to put in the loop would probably be the TA908e. It can terminate the PRI coming from telco and generate PRI to the PBX. You can manipulate parameters such as switch type and messaging, even peel off phone numbers to analog lines or SIP. I don't think the 3200 will properly terminate TDM voice.
One thing to keep in mind is that you will likely need to use a T-1 crossover cable for at least one of the connections regardless. https://supportforums.adtran.com/docs/DOC-5251 shows how to make one.