I'm living with full range speakers with subs right behind them, in a two channel system. Do I love the sound? Very much so, with a Bryston active Sub10 crossover. Never tried one sub, so for what it's worth, never tried one sub. From what I've read, the lower you can go regarding crossover frequency, the less the impact of one vs. two. I don't want to have to compromise, so if the price is right, go for two.