how to quiet down 3 inch exhaust

Resonator is auxillary muffler, normally glass pack shaped, that aids in sound cancellation.

I agree with the others, many of the glass packs out there are not much bigger then the piping diameter itself, so they don't eat too much real estate. Run as long as possible.

You might be able to run before Dynomax mufflers, or on the tailpipe just before the tips.

Secondary option would be some of Dynomax "VT" mufflers that use the internal valve http://www.dynomax.com/mufflers.php?muffler=vt or
Walker "Quiet Flow"
http://www.walkerexhaust.com/products/mufflers_QFSS.asp