If you are working with inductive loads, the capacitors will be required, regardless of which interface technology you choose. Without them, inductive spikes will eventually damage the controller. They appear as high voltage spikes at very low current, so they are not damaging at first. Over time, they will cause damage to various components. The capacitors will help reduce these spikes to more tolerable levels, but they are not easily eliminated. There have been updates to the USB communications module that can help reduce the interference. I would try the USB module and the caps first. If you experience malfunctions, then RS-232 can be used. You can even use a USB to RS-232 converter and communicate to the controller via RS-232. Again, this does not eliminate the problem, but we have seen this configuration eliminate the symptoms with a long service life. Typically, the caps are all that is needed for most people and the USB interface is a common choice as long as the caps are used. Hope this helps!