Umm... that actually wouldn't apply to gnome-alsamixer; that would be alsamixer itself. Man page here; -c indeed tells it which card to use, but that's handled some other way in gnome-alsamixer.

(Indeed, it should find a usable one, but thought it might be worth trying, in case the problem was specific to that one...)

Also, there are devices and cards; not sure which one it was... I'll try again when I get that back on.