The hookup guide has a typo, and the center-taps from your load sensors should be connected to "R" on the combinator (not "W" as specified in the guide). "B" and "W" don't matter as long as they're the same for each load sensor, ie. "B" is all constant resistance and "W" is all variable resistance or vice versa.

Hopefully that saves someone else from having to reverse engineer the circuit after soldering it incorrectly the first time.

With two half-bridge, three-wire load cells, you don't need the combinator. Identify the center taps and hook them up as S+/S-, and wire the remaining wires to their opposite colors (e.g. white to black, and black to white) and hook them up to E+/E-. The color-flipping puts the tension resistances on opposite diagonals of the bridge, so adding tension to them unbalances the bridge constructively. If you wire it up with matching colors, you get it backwards, and two half-bridges with the similar loads will balance each other out.

The four-wire load cell is two separate gauges, you can make a four-wire cell into a three wire half-bridge by hooking one wire from each pair together to make a common terminal.

This product looks so simple but when we started talking about it around the office lots and lots of people got confused. Thanks for posting and coming back to post your find. This board is really powerful once you understand that it's designed to work pretty much exclusively with pre-made scales, that it combines four load sensors (not load cells), and that your scale is often pretty far away from your Arduino (I need to combine these four things into one 4-pin wire). The Load Sensor Combinator comes in really handy once you've tried to build a scale or two.