On your CallCentric account page under "Preferences" you have settings for your DID's titled "DID Forwarding". There are settings there for where you wish to ring incoming calls to your DID numbers.
If you have a single DID your indicate under DID Forwarding that you which calls to the number to ring your primary account.
If you have two DID's and wish both DID's to ring the same phone make the appropriate setting under "Preferences" by setting both numbers to ring the same extension.
If you have two DID's that you wish to keep separate you would need to setup an additional CallCentric "Extension" and setup the new extension on the OBi (under SP2) to register and forward one of the DID's to the new extension.