With an open or mostly open system behind our engines they, IMHO, sound bad, like an unmuffled garbage truck.
I have made many free flowing SVX exhaust systems, singles, true duals, ones with an electric cutout and a dump pipe, with cats, without cats, systems with no muffler but five resonators.
There are mufflers now with a built in bypass valve to be mostly open at high flow.
I have not tried that one yet.