Integrate freepbx to auerswald commander basic

Hello to all,

I work in a small company which currently uses auerswald commander basic PBX (4 ISDN S0 ports and 24 analogue pots ports).

We need to integrate freepbx to the existing PBX to cut billing costs using voip provider and a gsm gateway.

My proposed setup would be:

I am planning to connect the two ISDN s0 ports to an OPENVOX B400P card in the FREEPBX server and the rest two ports of the B400P card with the commander basic ISDN S0 ports as TE.

My main concern is whether the IVR of the freepbx can redirect the calls to the POTS extensions connected to the commander basic PBX. How can someone redirect the call after the IVR to the selected POTS extension? Maybe multiple DIDs should be defined each corresponding to the specific pots extension?

Would it be better to interface the freepbx server after the old pbx through FXS/FXO cards? (NT-> COMMANDER BASIC PBX-> FREEPBX SERVER)

Another requirement would be to seamlessly bypass the freepbx server and use the old architecture in case of problems.

If this setup succeeds we will use it to integrate the pbx in the HQs so I need to make sure it works. Please express your opinions and also if you have had similar experience with auerswald commander basic pbx.

Thank you in advance