I haven't said SID is superior, as I tried to explain, both chips are unique and incomparable.
Digidrums on the SID scene mean nothing, specially for the SOUND, otherwise everyone will use them today, and instead, they chose not to, because they really sound like shit and add nothing to a piece.The evolution came in other aspects, and right now, they are, luckily, more "musical-oriented" than trying to be "technical orented". Some people with C64s today, the ones that I think are right now the most important for the future of SID music, are aware of what the SID is and what it can do, have the technical know-how to do with the chip whatever they want, and they use all its capabilities to create new music, real music. Some other people like to compose exactly like if this was 1986 and immitate the works by people like rob Hubbard. They do nothing for the "sound of the SID". Trying to make a chip imitate another is lame, why not use your unique chip's good and bad qualities and really push it? I have barely heard stuff for YM/Ay chips created with this in mind, this is not to blame on teh chip, but on teh composers!
I bet *might* be possible to make a ZX do that, I don't know, but as I said, it probably is a byproduct of the ST being clocked higher. Same thing as a SID inside a SIDstation.