Can you tell me a little more about how your install? Is only the new sub powered by the new amp? You replaced the other speakers but they are still powered by the factory amp?
The B&O systems in the 2018 and up Fords use a serial digital protocol to between the ACM and the amplifier, so simply replacing the amp is not an option. PAC is releasing the AP4-FD31 as an interface module to allow seamless integration of an aftermarket amplifier.