^ this. A lot of the orchestral music in the fandom strays far from the traditions of Classical music in terms of structure, arrangement, tonality, blah blah. I'm not sure I've heard any real "Classical" music in the fandom! (It's probably out there.) If you were to condense the two into one tag, Classical/Orchestral, that might be enough.
On a very literal level, a lot of what I would refer to as IDM is indeed electronic music that makes you dance, and should *theoretically* be able to be called EDM. Buuut, EDM is used to refer to specific kinds of electronica generally made for club settings - including house, dubstep, and all their myriad subgenres - but not to what I would call IDM. Basically, I mean any kind of modern-ish electronica that wouldn't be played at a club! (Compare tracks from Archie or Aviators to those from
,
, or
, and you'll see what I mean.) I think we need a genre tag for this. "Electronica" would suffice if it came down to it.