Todd, welcome. Assuming that you're referring to a sub with a built-in amp, there're two possibilities. Since your 352 has no subwoofer output the simplest procedure would probably be to connect regular speaker wire from the 352's output terminals to the high-level speaker inputs on the sub(assuming that it has them). These speaker wires to the sub would run in parallel with the usual speaker wires going from the same terminals to the monitor speakers(trim the ends of the wires if necessary to make them fit the terminals). Depending on the sub, an alternative connection to the speakers could be made if the sub has high-level speaker outputs for them, but you haven't described the sub that you're considering.
Your 352 also has a second set of left/right pre-outs which could possibly be connected to the sub with two coaxial cables if it has left/right line level inputs(the use of a Y-connector at the pre-outs to feed one coaxial cable is controversial and could cause problems).
Since the 352 has no bass management provisions the monitors would run full-range(unless the sub would happen to have a high-pass filter to the mains)and you'd use the internal sub crossover adjustment to roll it off at a frequency where you judged that it blended well with the mains.
