Board Thread:Questions and Answers/@comment-66.66.129.84-20130104024106/@comment-5796218-20130104030917

You can pipe everything into a chest first and then hook a Sorting Machine up to the other side to pump things out of the chest and into the tube network in the groupings you want. Set the Sorting Machine to all-stack sequential mode, color code a few columns (pick different colors) and then place the quantities of the items you want to split in each column (aka the "stacks" in all-stack sequential mode) in the GUI. Pulse the Sorting Machine with redstone to have it pull the first set of items out, color code them, and dump them into the pneumatic tube network. Pulse it again to move on the next stack, color code it, and dump into tubes. Rinse, repeat.

Make sure to color (with a Paint Brush ) the target ends of the Pneumatic tubes so the colored items know where to end up.