I don't know anything about the 978's bass management, but I can tell you that you can still use your sub even if there is no analog bass management. Just run your fronts full range with the sub. Now this results in what people call "double bass" but its not necessarily a bad thing. In fact, although I have the 950 which has analog bass management, I've actually achieved a flatter bass response in "double bass" mode than I have with the analog bass management enabled. The trick is getting the speaker locations, phase, and crossover settings right.

But - this is why I think its so critical for the pre/pro to have a great DAC/analog section. Its just so much easier if the pre/pro can manage bass in the digital domain. And you get the extra benefit of not having to spend $$$ on source gear with great DACs/analog peformance.