I think the gold cube is a great machine, its just that it takes time to classify down to 8 mesh. There's trommels you can put on top to help. Its just Don't expect to run a bucket a minute with whatever setup you choose.
IME and never having used a hopper, but have recirculated with a A 51 sluice, the only way I see it recirculating is if the material was already classified to 8 mesh. I would think the hopper would need to classify to 1/8 mesh, but most hoppers I've seen won't go that small. I've went up to 3000 GPH with my A-51 and it still wasn't enough to push 1/2" stones through using both ridged matting and another run with 3/8 punch plate.
I only bring this up because I spent a lot of money and time on dumb ideas, most of which were my own.