I haven't heard the M50 or the RX700/900 so I can't comment on their sound, but the D2000 sound, even unamped will be fun for movies. It does benefit a good amount from an amp, but I think you would also enjoy them plenty without, or out of a receiver if you have one.
Hmm, not sure how well it'll fit your music preferences. It would depend on what you're used to. If this is your first pair of "good" headphones I think you'll be pleased all around. If its not then you might be a bit more discerning. They'd do pop well, electronic would depend on what you value of the sound (I know some prefer D2000 sound trait for it, and others that like pretty much the opposite), alternative rock will be good (although there are ones that do it better, I don't think those would be as good as the D2000s for movies), and I think classical they're not great (but again, if you're not used to decent headphones you might think they sound quite good).
I would maybe say give the JVCs a try first, they don't cost much and will give you some reference. You could then maybe have a better understanding of what you'd want. I mean for that price you could actually probably get maybe 2-3 headphones to check out, or use the extra to get a better source (sound card, DAC, etc).