Speaking as someone who knows almost nothing about pop and rock and far, far, far too much about classical music this thread has been an education. What do I take away? There's a lot of skilful musicians out there - Flight of the Bumble Bee on electric guitar takes some doing. There's a lot of tosh - Andrew Lloyd Webber is a terrible advert for classical music, and having him performed by a belter rather than Sarah Brightman doesn't improve him. The best responses to classical music in different genres are those that take it on its own terms - I never thought I'd see a Scandinavian heavy metaller sing Puccini absolutely straight (and it is absolutely straight, even when the guitars come in with a spurious third verse) in a stadium.
For me, the most successful two numbers in this thread are the Ska Tchaikovsky and the electronic Holst's Mars. Tchaikovsky's a seriously over-rated composer and you need to do something to liven him up - why not a Ska beat? Both that and the Mars (and, for that matter, the bits of ELP's Pictures at an Exhibition that I managed to see before the video crashed) are essentially straightforward arrangements.