There is only one chart with Bukit Siguntang, as follows.
It does only north-south, between Kupang and Nunukan. It is unique in that it does not dock at Surabaya or Jakarta, at all.
Quite how useful this boat is, I am unsure, but it may serve as a reserve ship for going further south from Maumere.
Now, we have seen three boats linked to Maumere. It is disappointing that none of these boats actually goes to Ambon. That is to say that it is not possible to reach Ambon direct from the south, from the Banda sea chain of islands.
Makassar is a hub, of course, but it is not the hub for Ambon, because you can easily reach Ambon from Surabaya in a few days. Almost the same nautical distance from Makassar to Ambon, anyway.
However, if you fly Makassar, then ferry Ambon then it may be something to consider further...
Case closed.