There are many routes to satisfaction and some appeal to different people differently. Still, in this day and age of sophisticated bass management and roomEQ/subEQ, some traditional configurations might be reconsidered. In fact, one can probably get better, more integrated, more even and more convincing bass from 2 mono-signal subs, placed carefully and balanced/EQ-ed properly, than from stereo subs whose placement is constrained by the placement of the main L/R speakers.
There are a few relevant "white papers" from Harman on this.
Kal