I agree with David, if music is the priority, then it won't be a good buy,if it's going to be used 50/50 for music and movies then maybe it's worth considering. For £400 (incl. delivery) you get the XLS300/PR which goes deeper than the 200, but has agility that the Monolith won't manage, even if the 300 can't manage the depths of the monolith.
What front speakers would you be using it with? An AV amp to set the crossover (lo level) or a stereo amp using the hi level connection? Do you need a huge beast like the Monolith, how big is your room?