The same board(s) that were being used to support Cornet can also handle a PRI circuit. Only the AMO config is different. But if you are determined to connect to a PRI via a SIP gateway, then a STMI2 or STMI4 is required. The STMI is configured via AMO to support Native SIP. The web-based management of the STMI is used to connect to a Mediatrix gateway (model 3631 in the USA). The Mediatrix then connects to the PRI. The Mediatrix converts from Native SIP to PRI. This feature was originally designed for Softgate, a Linux-based IPDA shelf that uses "virtual" boards (vSTMI) rather than physical boards. Therefore to install PRI trunks on a Softgate, a virtual STMI is created, connected to Mediatrix, which is connected to a PRI. If you do have have Softgate, I would recommend supporting a PRI using the conventional technique: a DiU2U or DIUT2 board connecting directing to the PRI. This trunking hardware is rock-solid, where I cannot say that the Native SIP to Mediatrix is "rock-solid" because it involves third-party hardware & software to function.
Which card were you using to support the Cornet? You can type this AMO command: DIS-BGDAT;
It will show all of the supported hardware by part number for your specific system. It also provides some config tips, such as the Function ID (FCTID) and number of channels per board.
I previously recommended training for you, too. What happened? You could be handling this work by yourself without having to spend months of plug-and-praying! Attend training!!!!!!!!!!