tubesaregood said:
I would probably run low level to one and high level to the other.
That is not a very good configuration. Consider those who use the crossover in the receiver, it is the most practical way of setting a crossover for a home theater. If you had the fronts set to small, as they should be, and the crossover in the receiver set to 80hz, around were it should be, then you wouldn't get any use or very little out the sub that is using the high level inputs. It would only go as low as 80hz and it would start to rolloff. Not only that but it would increase the probability of frequency nulls and boominess because your front speakers would be playing those same frequencies.
The Y-adapter is the best and most practical solution, first to using low level output on select subwoofers to daisy chain. Daisy chaining with cost more on interconnects, hence not as practical.