bose 997 no bass

[chocolate engine]

my battery went and the stereo stopped working after it crackled a bit.
anyway i had a look and ended up replacing the amp of the same part number off another porsche
plugged it in and up it came but the bass was not working in the back
it on a fbre ring so i took it to the dealer and they had no idea why its not working as it shows no system errors
anyone got a clue before i start taking things to bits?

[markiii]

Bose sub has its own separate amp, tiny little thing, part of the sub assembly

Maybe you blew that too?