Shadorne hit the nail there. It all depends on the room. If your room is huge I would say go for three way with large drivers as opposed to small monitors and a sub. If your room is small, monitors with a sub is the way to go. I have monitors and subwoofer configuration in smallish room of 11'x17'x8'. The 4" drivers of my speakers are rated at 35Hz but the bass roll-off at around 60Hz in my room. The subwoofer really helps in fleshing out the bass and just like Xti16, this made a huge improvement to the sound of my system.
If your room is to the smaller side of things, I would highly recommend that you add a subwoofer to reinforce the bass of your system, more so since your monitors can only manage 80Hz. In reality they would roll-off at a higher frequency due to placement from wall boundaries. The quality of the subwoofer plays a part too as inferior subs with large drivers may not perform as well as high-quality subs with smaller drivers.
If your room is to the smaller side of things, I would highly recommend that you add a subwoofer to reinforce the bass of your system, more so since your monitors can only manage 80Hz. In reality they would roll-off at a higher frequency due to placement from wall boundaries. The quality of the subwoofer plays a part too as inferior subs with large drivers may not perform as well as high-quality subs with smaller drivers.