I'm not too familiar with the ZX, but if you can get a bullet type under the car shortly after the tranny, that will help. A typical S30 system would be something like downpipes into a single 3" pipe, into a bullet style muffler, into a 3" tube into a Flowmaster or Dynomax Turbo muffler, into an exhaust tip. Or from the downpipes, into an X pipe, into two bullets OR flat Spintech or fairly flat muffler with dual in & out, then dual pipes back to a dual in dual out muffler out back or two mufflers side by side out back. Feh, this is getting complicated (I hope I typed it out correctly).
Just put two mufflers in the line, essentially, and you should cancel out most, if not all, of that droning.
Davy