With regards to the droning issue on a VY V6 ecotec wagon with a free flowing "cat back" system, are there any other options? As in a free flowing, relatively quiet rear resonator that would address this?

It would. However now that I think about it, your best bet would probably to run a factory 2 1/4" twin system from a VZ alloytec wagon or from a VT to VZ V8 wagon. Please note though that you would have to modify the pipes from the headers such that you can run twin cats. To avoid drone, I would also stick with factory cats