Don't know much about that particular route, but i just arrived in Brazzaville from Pokola (near Ouesso) after 13 days on a barge down the Sangha and Congo rivers. It was an awesome experience, like a floating village market. At every village people paddled alongside in canoes to trade goods and we accumulated all sorts of animals, living, dead and smoked. The tiny deck space was littered with live turtles, catfish and crocodiles. The people were great too, the friendliest i've met so far in Africa, although i struggled not speaking French or Lingali.
I bought my own food before leaving (spaghetti, rice etc) and cooked myself, but it's possible to buy stuff en route and have it cooked for you by the Mama's who trade on the boat, that is, if you like smoked fish and manioc.
The only problem was the time. 2 weeks is much too long to traverse 850 km. The problem was mostly in the Sangha which is difficult to navigate due to sand banks. We zig zagged the entire length of the river, but nevertheless got stuck on a sandbank for a day.
My tent (fortress of solitude) came in very handy. I set it up on the top of the stack of wooden boards that was the main cargo and wasn't bothered by wind or rain.
To catch the boat i just turned up and paid 30 for me, 50 for the bike. Travelling by boat with a motorcycle also has a lot of hidden charges connected with the loading and unloading. Expect to pay between 6 and 20 dollars each time you need help to unload/load the bike.
I highly recommend the trip though if you've got ime and patience.
Sean