I've always heard of it as the 9 principle spiral horns. There are so many subspecies that you could really sidetracked, though. The 9 principle spiral horns would be:
Bongo
Mountain Nyala
Common Nyala
Sitatunga
Bushbuck
Greater Kudu
Lesser Kudu
Lord Derby Eland
One of the other Eland (Livingston, Cape, etc...)

I guess except for the Mountain Nyala, Common Nyala and Lord Derby Eland there are several subspecies of the others so you end up having "slams" of Greater Kudu or Bushbuck, whether they are recognized by some record book or not. There are at least two subspecies of Bongo, maybe 3? I can't recall how many different subspecies of bushbuck there are, but it's about a gazillion...