I don't know if it's only my everdrive or all of them, but fds audio is insanely unspeakably bad. I don't think that it's my copy of everdrive, because Gimmick (with custom mapper) and Akumajou Densetsu sounds great in other hands. I can make a comparison with real FDS if you want
edit: i would say that it's even better to play games without FDS extra sound channel