I highly recommend going with a pair of subwoofers. Even with an 80hz crossover I can still get a bit of directionality with just one sub. Two subs will also give you higher output. I am using a pair of smaller subs with a Richter Scale EQ and Sony TA-9000 amplifier bridged.
When used with my Inifinity IM 4.1 that have their own sub built in as well I experience true room lock like I have heard with no other system.
