You can build hay feeders that reduce hay the hay waste. But if the hay is incredibly tough and stemmy, no animal will want to eat the stems. They much prefer softer hay, if that makes sense.
Just keep an eye on their weight with the reduction in grain and the pickiness with the hay. If they start dropping weight, then you will need to add something. Either more hay (despite the waste) or more grain. They always need to have hay to have a healthy rumen, but they also need enough calories to be healthy as well.
What are you giving them for their mineral needs?