Best thing to do is high pass your monitors. If you're worried about quality loss going thru a subwoofer's crossover, your best bet is to get a really nice active crossover. Marchand, Bryston, Pass Labs, and JL Audio come to mind.
Generally speaking, you're not going to get the best performance from a lowish powered SET with normal multi-way speakers. It isn't just a matter of speaker sensitivity, though that's a large piece of the puzzle. Personally, I would reprioritize gear selection (based on listening habits and preferences) before getting into active crossovers and other complications.