I am glad you too are convinced, that Pitts mufflers realy are no good for gas two strokes. You would also be surprised at the temperature difference in the running engine. My TD90 system has better throttle response though.
Even better are the new 4-chamber canisters that MTW is working on. 200 rpm gain over the 3-chamber mufflers, and MUTE like my pinched header with 100 rpm loss.
I had a chance to test one very briefly before I had to pass it on. Tonal characteristic much like the very much larger, heavy and well muffled JMB. Where the JMB tended to overheat the engine, the MTW was very easy to adjust the carb to, without the slightest rpm drop. All with outstanding throttle response. A stroke of genius, though the 4-chamber design will probably be a bit more expensive to produce.