No reason not to have a quality sub. An SVS Pro is an affordable quality option that has a dedicated iphone app that lets you adjust the EQ, crossover, volume, etc to your liking. I use different saved settings for music and video. I also adjust it based on the particular album I listen to.
Why I'm not adding a sub to my 2-way monitors for music
I've updated my blog post with more data, more analysis and the conclusion that in my particular case I do not need a subwoofer. I encourage everyone who is on the fence about adding a subwoofer or not to read and comment. I think that either way you'll be able to make more informed buying and configuration choices.
Everyone's situation is different but I hope the post helps you get to the right conclusions.