Phasecorrect, what do you mean when you write, "... stations are using hybrid digital-analogue signals in FM mode?" If we are talking about radio in the US, standard FM audio is analog although, of course, it may have been digitally processed.
If you're talking about iboc "HD" radio, that's purely digital. It's licensed by iBiquity, which says "HD" doesn't stand for high definition, hybrid digital or anything else.
HD radio technology is pretty much a dead-on-arrival technology in the US.