If you are using a pre 5.1 receiver (one without a sub-out): you'll need to run the speaker cables through the sub for a low-pass filter. This is less than ideal but what you have to work with.
If your receiver has a "sub out". Use that. Set the crossovers around 90Hz (feel free to play to find what works best, assuming the receiver lets you change settings). Also, if the sub is a bit "boomy"; remember that can be fixed for $3.
Remember as well, if you are using a "sub out" on the receiver, set the crossover on the sub itself to "bypass" or, if that options not on it, to as high as it goes.
For ideal listening, you'll eventually want a second sub, and an external crossover. This will let you use the two subs and 2030's as a pair of full-range speakers.