Studio monitors give a fair representation of what the music SHOULD sound like... an easy contrast would be something like Beats By Dre, which have a massively ''colored'' bottom end, meaning they have lots and lots of very loud but not very detailed bass. Studio monitors are made for music producers to be able to hear exactly what their music sounds like, without any of that dreaded ''coloration''. Usually these monitors are very very detailed too, which means you can pick up tiny intreancies in songs you wouldn't otherwise notice.
As for an external sound card, the problem with Fiio products is that they're very much geared towards the headphone and portable market, which usually means they aren't AS good at running speakers in general. What you're actually looking for is known as a ''DAC''. This is basically an external sound card that do normally sound very, very good and are (in my opinion) preferred because of the fact they're external, they negate any electrical noise going on inside your PC... had massive problems with this with an old xonar DX.
EDIT : Having said all this, I actually think you should go DAC < Speaker Amp < Bookshelves, since you're looking for something for movies and gaming, not just exclusively music.
