I would also agree that active crossovers make a huge difference. However, I would like to say that I have the cx3400 currently in my setup and am smothered with quality problems. For instance left channel mid looses proper output until warmed up and then works correctly. The limiter feature kicks on as a hard clip instead. The adjustments are not very accurate. The list goes on. As far as the good; it sure does come with a lot of features for very little money. And it does work good and sound pretty well. Spending some extra money with better reliability would be a good idea.
When the cx3400 was new I had no problems with it whats over, but after a year a whole bunch of problems started to show up. Good but still inexpensive choices are dbx 234, rane ac22 or 23, etc.
Not trying to bash any ones gear but spending a little more might last you and serve you better in the long run. I sure do wish I could have made the right choice the first time.