There were 2 problems - you were hooking up multiple speakers to one source. If the speakers weren't bridge inputs (inputs that put no load on the device they're plugged into) you overloaded something in the phone. And that old superwoofer was probably defective, and probably fed some DC voltage back into the phone. (Also, plugging and unplugging powered audio devices in and out is one of the""bad ideas". Turn everything off first. It sounds cool at a show, when the bassist plugs in live and the speakers howl back from a guitar string. But they're getting paid enough for that gig to replace a speaker or amp.)
Your only option at this point is to (bring the phone to a shop and have them) determine where the damage is - the jack, the wires or the motherboard. The jack and wires are replaceable and not too expensive. (If it's a burned out wire you might see a "parts" charge - but you probably won't.) Please don't try to "save money" by doing it yourself. Fixing the things you broke when you did it will cost a lot more than the original repair would have.
If it's the motherboard? Well, it's a GS4, so it would probably pay to have a new one put in - but it won't be cheap.
Next time, use the earphone jack for what it was designed to do - have earphones plugged into it.