Varex looks promising if you like the loud sound at times, then can flip the switch for quiet

If you want to avoid loud at all times, use a resonator for power, along with a regular muffler for quietness

Here is the factory GX system



But something like this may be better, attached directly to the resonator



For racing, if allowable, they use no muffler at all. But if you put a resonator at that point it is nearly equivalent. Then adding a full exhaust pipe & muffler makes no difference to the tuning. The resonator effectively terminates the exhaust system as far as length and tuning goes