I have no solid info in this route, sorry. Last I heard was that Congo is still very unstable (violence) in the eastern and southern region. Especially in the Kananga, Bukavu, Kalemi triangle. This info dates from the last time I investigated the possibilities of visiting congo (about 6 months ago). Situation might have changed in the meanwhile.
I was planning on just crossing DRC in the west at the coastline which should be safe.
If you plan to do this route, you'll probably have to make your own way, not a lot of tourists have been there in the last decades.
Keep us updated if you find some info on this route, it would be greatly appreciatd!