Aparantely the "root net" serves as soil, so the seeds can grab. It's very similar to a post i red here as well, which uses nothing but water.
There is also this
, no medium whatsoever, but i don't like the fact it's closed of so natural light doesn't come in play plus it's expensive - you'd need quite a few of this for 3 people to have wheatgrass daily. I've red several posts here people using pure hydronics, no mediums what so ever.
PS If i havent mixed up something, you use sunflower greens, right? Do you juice them or eat them as sprouts?