From my romantic-ecological point of view, I always prefer to give my animals (birds, reptiles , roaches etc.) the most 'natural' habitat conditions. As for roaches , I simply put rotten leaves and rich, humic soil (collected from an oak wood near my home) in their plastic container . That's all. This is not a sterile 'substrate' but a little universe populated by million microscopic creepers. (That's BIODIVERSITY at his best!) . As my Polyphaga species live most of their life underground, I like to think they enjoy the company! Moreover they don't eat any kind of 'commercial' food I give them.
So, I suppose all these micro-critters will produce good pre-digested leaf and wood stuff for the roaches to eat.
p.s I added some Trichorhyna for best , bought from the man named EffeCì.....
romango