I used to be skeptical about YouTube videos and audio. However in my real life experience, it does give a pretty good representation. For instance, I owned the Sonetto II speakers for a while and they did sound like this video
I definitely am curious about class d also. Since I heard class a and fell in love with it at the Hi-Fi shop, I know I like that so starting with that. Especially when the cheaper integrated class A's are no longer on the market, they seem to be discontinued. I would have to go to monoblocks for class a which would be really expensive and not what I want.
But later on, I do plan on trying the techniques r 1000. That's really the only class d I would ever go for.