I've crossed DRC by bicycle from end of July to end of August, from Kinshasa to Bukavu. It's possible, but really hard.
From Kinshasa, you've more than 600 km asphalted. Then, it's only sandy roads... Every day, I had to push my bike several hours in the sand with guys who carrier 200-250 kg of goods with their old bike. The part to go to Tshikapa (and to Kamuesha) is really sandy. Then, you've about 120 km of "acceptable" non gravelled road to Kananga and 30 km of asphalt ! Then, it's going to be sandy again to Mbuji-Mayi.
DRC is the country who has probably the worsth condition of life and of travel: no electricity even in town. It is a very interesting country, although I think this is not a country to practice conventional tourism. However, the DRC incredibly well prepared to travel, to explore. So many things, so many scenes seem unimaginable and surrealistic even event if you compare them with the countries around.
Good luck for your trip