For me, Opeth used to have this "orchestral" vibe. Interestingly, it was only back then when they didn't use keyboards and just painted nice walls of sound with their guitars only.
I mean songs like: The Moor (that intro, starting at pp and getting louder, reminds me of how quite a few classical symphonies start), Drapery Falls, Blackwater Park, April Ethereal.....or evel older stuff like A Nigth and the SIlent Water (these would kick ass if they got the whole orchestra treatment).