I highly recommend Lubumbashi.  You can get there from Kinshasa by Congo Airways, which is about a two hour flight (though a bit pricey).  It’s a new airline, and I can’t get over the Christmas music that plays every time you board and disembark from the airplane, kind of like the Brazzaville bridge lights that wish you a Merry Christmas and Happy New Year every evening.  Oh, and that someone’s phone went off mid flight.  How did that happen?  I’m still not sure.