Well according to the first 2 minutes these strings don't seem too "far fetched". But they sound like they came out of something like the EWQL plug-in, the quality seems nice. There are like 1000000000000 and I just decided to do like everyone and get the EWQL.

But if you really have to go only the free way I would browse through a lot of string orchestra plug-ins and decide the one you like. And they sound like only one string orchestra so it's quite easy. And personally I think that such "metal strings orchestras" should have a very quick attack and I like it when they have a long release. And there's too many subkicks in that song.
And then how to make it fit with the band, well it depends on the frequencies already used by the band. Example, the guitars are strong around the 1200 frequency then I would remove some 1200 frequency in the strings. Kinda like a puzzle? And I would personally try many panning alternatives but something around L50 and R50 should work. If you pan it more in the center it might sound too little when the band is not playing ( if that happens ) and if they are more to the sides then, the band might not give the uber boomba that it should when it kicks in.
ps : I know there is a topic somewhere in this forum that links a lot of free plug-ins but I can't find it right now and I am hungry.