it is not so much an even amount of junk. with advanced insertion pipes there is no need to give them an even amount. the junk will just cycle round until it meets a recycler that can accept it.
If you really want to give recyclers an even amount of junk go for distribution pipes, then you can assign even ratios for each recycler (takes forever, really boring ) so that your request works. However the only issue with this is that they don't take into account different types of junk, so if the distribution pipe decided a plank was to go into a recycler that was currently doing a large batch of cobblestone, it would pop out, unlike with advanced insertion pipes.