I think there's a great case to be made for multiple subs, but in MOST rooms, especially if mostly near field listening, you really can easily get away with one...if it's a well designed sub like REL makes. "Aural cues" that determine soundstage accuracy aren't in the bass domain really, and note that a REL sub when utilizing the "high level" signal from the power amp won't relieve the main amp's task, but will certainly SEEM like it is. I have skinny tower speakers with a front firing REL behind one speaker and it loads my large-ish room just fine...a lucky acoustic profile in this room helps everything, and I do have to adjust the sub level here and there.
