In a nutshell,
your ARS Digits Dialled will say:
911 --> Route List 9
Route List 9 will contain Routes 91,92,93,94,95,96,97
Route 91 routes to Carrier A, COR Group 91
Route 92 routes to Carrier B, COR Group 92
etc...
COR Group 91 will allow Site#1 CORs only
COR Group 92 will allow Site#2 CORs only
etc...