Hard for me to imagine having another sound other than game sounds piped in while playing. I rely heavily on sound to know what's going on around me! I guess if I didn't have directional sound it would be different.
I got into mmos with Dark Age of Camelot. When that came out I had Flaw's first album and the Fellowship of the Ring's soundtrack on all the time playing it. With this game I wanted to revisit that nostalgia, but I added every Hobbit and LotR album with every Flaw album and some Dragonforce mixed in. Been loving it.