Option 1 -- DIT the CO lines to the paging port, but when you do this the calls will never forward to voicemail. I usually setup a Night key for after hours in this configuration. The phones will ring based on the ringing on the CO line keys on the phones.
Option 2 - Get a PI-DKT from page industries and use a digital port. https://www.pageindustries.net/index.php/page-port-adapter/pi-dkt-r.html
Option 3 - Get a Viking PA-2A and connect the CO lines in paralel. https://www.vikingelectronics.com/product-details.php?pid=317
Option 4- (Assuming the page amp has ringin input) Add an ASTU1A to the CIX 100 and configure a multiple call group.