There are rods that easily go through 90s in 6" pipe. I dont know about the soot eater rods though. I do it with ours all the time but they cost a little bit more than sooteater.It's not the 90 degrees that kills you. It's the bend radius you use to get that 90 degrees. I do not think you could shove a sooteater through a 90 degree tee or 90 degree bend in a 6" pipe but you can go into the door of a stove and up through a top exhaust just fine which is also 90 degrees but a much larger bend radius.
I've snapped one rod while trying to push the sooteater through the stove and up the chimney from across the room with like 4 rods attached, I was getting lazy. Pushing towards the stove bent the rod too sharply and it snapped.