A support engineer from ADTRAN provided the following guidance:
I would recommend the first option in grouping your PRI's such as the following:
connect pri 1
connect pri 2
connect pri 4
connect pri 3
This will avoid any call loops (therefore bypassing the need to run Source Ani Based Routing (SABR)).
I would like to point out, though, that PRI to PRI is not a supported application. So while it can be configured, if there are any issues with the operational capacity of the configuration, we will be unable to assist in configuration changes or troubleshooting. If you have the option of running PRI from your carrier and then SIP to your PBX (or vice versa), it would be recommended to take that course.
Further clarification was given:
The order that the PRIs are connected will determine how the channels are allocated. This can be somewhat manipulated by changing the 'resource-selection' command which is detailed on page 4,668 of our AOS Command Reference Guide located at the following URL:
AOS Version R13.6.0 Command Reference Guide - https://supportforums.adtran.com/docs/DOC-2011
Perhaps this will be helpful. Thanks, adtran-support!