Soybeans are a legume and as a legume matures, it increases in ligin content. Ligin is not digested in the rumen. From a quality standpoint, baled soybean stubble would have a nutrient content similar to straw or less. It would be about 4% crude protein and likely less than 40% TDN. It could possibly be used in a mid to late gestating beef cow ration to stretch some high quality forage source like alfalfa. Would recommend that you grind the bean stubble and then mix it in with the ground, high quality forage for best use.
Corn condensed distillers solubles from an ethanol plant solubles are high in water, protein, energy, phosphorus, and sulfur. Solubles could be fed with soybean stubble, but I would not feed over 7 lb/hd/da (if solubles are 30% dry matter that = 23 lb/hd/da on an as-is basis) of solubles on a dry matter basis. Solubles a high in phosphorus, so you would not need to supplement P.
