Connect Astrisk to existing PABX via ISDN card

I’ve got an existing NEC phone system with spare ISDN line ports and I want to install an Astriks/Elastix box to act as another line to make and receive VOIP calls. We’re starting with just a couple of IP phones/Soft phones with the plan to expand to a fully VOIP phone system in the future but for now we just need the NEC system to use Astrisk as a VOIP line.

My question is, am I able to install a Digium TE121 ISDN card in Astrisk and configure it as an extension that the NEC can dial out on using one of it’s available ISDN Line Ports?

I’m using the latest version of Elastix as my Astrisk box. I’m very new to Astrisk so your assistance is much appreciated.