Greg, I believe your definition is probably as good a one as has been written. Canisters that are manufactured have exactly what you're talking about. The reason they have "tuning" effects is the restriction of the first chamber created by the baffling separating the input tube with it's holes from the expansion chamber with it's exit nozzle. There a some pretty dang good "do it yourself" canister plans floating around made from a variety of things, but nearly all of them meet the "tube with holes, baffle, and expansion chamber" definition.

I have not had the large volume Pitts from J'Tec, but have used (and still do) the "standard" volume/size for the DL 50. I think it has a much mellower tone than the stock muffler, and doesn't rob power from being too small. My experience with Slimline is that they are fine quality products, but tend to be a little small in their chamber sizes, and when I've used them, reduce rpm by restricting too much. Others have reported other experience, so there may be differences in perceptions or expectations.

If you are flying someplace where loudness is an issue, or will be, I'd recommend a canister/header setup from the get go, whether it is a purchased system or home-made.