As many resonators as can fit, plus be sure to have the largest muffler possible. I had one with the larger oem style muffler but the tip was 4". It was better than the cannon muffler style but still fairly loud. Got the invidia Q300 and it was a little better because better muffler baffling.
This time I'm getting several resonators and a large Apexi universal muffler, all done together. It will still be 3" minimum pipe all the way back, so long as the resonators and mufflers don't reduce diameter it shouldn't affect power enough to notice.
Resonators are pretty much tiny mufflers, so they just mellow the tone even more before it gets to the muffler. There is limited space under compact vehicles, so anywhere they can cram additional muffling is advantageous.