OP, if the amp is a servo, it relied on feedback from a sensor on the driver to make near real time correction. You may not get the same performance with a standard subwoofer amp regardless of the controls it has.
Now, this doesn't mean an aftermarket amp won't be good, but it's likely you won't get the performance out of the driver that you would with the OEM amp.
Now, this doesn't mean an aftermarket amp won't be good, but it's likely you won't get the performance out of the driver that you would with the OEM amp.