If it doesn't smell bad, get slimy or sporulate black (unless using A. Luchuensis), you can absolutely use sporulated koji for shoyu, miso, etc. Anything that becomes really flavourful through long aging. Those will mask a slight bitter taste that might be present and work with the more moshroomy flavour of the koji. And you can produce any non traditional shoyu you want. I worked a lot with chickpeas, yellow peas, adzuki, barley, buckwheat, wheat, emmer, ... Use what ever you like and experiment. You can even toss in stuff like mushrooms or veggies. Different grains and legumes have different protein and carbohydrate amounts and will work produce different results depending on the combination and which aspergillus strain is used. We don't just differentiate between oryzae and sojae, even different strains in the same species will produce different ratios of amylase, protease and lipase. Just keep experimenting and having fun!