On the X series, the main amp does not "go through" the subwoofer amp. They are wired in parallel. Which means the main amp drives the mid/tweeter drivers directly, and also drives the sub amp directly (hence the term 'parallel', haha).
If the sub amp lights up but you're not getting any output from the woofer, the first thing I would do is check the wiring as it's probably something just came loose. Remove the sub amp from the back of the speaker and look/verify that all wiring is firmly connected and nothing has worked loose.