The Caprivi is primarily a DG area. While red lechwe are locally common on some few concessions, very few are available on anyone's quota. A very few roan and sable are on quota, but most outfitters reserve them as part of packages for clients hunting DG - particularly elephant. I know of no conservancy with sitatunga on quota. The plains zebra in Caprivi are quite beautiful, looking a lot like mountain zebra - most lack shadow striping.
But the big thing in theCaprivi is DG. It is a rare and wonderful place to be, and I could not urge you more to try to find the means to hunt a buff while your buddy is sitting for cats. I suspect your outfitter may be open to some sort of negotiation ondaily rates since you are already booked.