I don't have the tech chops to comment on much of Curls ideas on capacitors and such but he is probably right the the best cap is no cap whenever possible?
I do and I have. Another one of those "there's a germ of truth, but it's been completely blown up into something it's not" deals. Curl took the correct idea that some dielectric types have higher DA (dielectric absorption) than others into the notion that this somehow makes low DA caps better for coupling. This is what started out the cap rolling craze. DA is important in timing circuits. It is absolutely irrelevant to coupling caps, and I've posted measurements to prove it.
For caps used in filters, there can be some small measured differences between dielectric types, but once a certain point is reached, it's not terribly relevant. For example, polypropylene (cheap) will measure better than polyester and is preferable. Polystyrene (more expensive) is slightly better, Teflon (extremely expensive) slightly better yet. But PS and Teflon both have major disadvantages which don't get considered by the cap crowd, and of course, polypropylene already gets you to the point where the distortion is beyond negligible.
Of course, all of this is dismissed because "everyone knows Teflon sounds better" or somesuch. Here's a list of actual controlled listening tests supporting these claims:
Oops.