I've been adding a cup or so of spent barley to each loaf, left over from mashing home brewed beers. This adds a wonderful taste, texture, adds moisture and greatly improves the crumb. My wife insists I do this every time now.
If you don't have access to spent malted barley, then I urge you to look into home brewing you own ales. For one who enjoys the lengthy process of SD baking, home brewing is a natural and heaven sent hobby!
I have a local organic brewer giving me his spent grains. I concur that they are well worth adding in. They add welcome layers of flavour that go very well with all sorts of bread.
Also, I have been soaking dried out rye-wheat (50-50) loaves (baked in my brick oven) and using the resultant crumb (about 15% baker's percentage) in the dough. That gives an enormous kick flavour-wise, almost like adding in port or cheese. I recommend this too. Plus using the water from the soaking as well.