Thats good you have no liners, they put off alot of cats so i would have said remove them. The one per cat plus one is a behaviourial rule for multicat homes and its applied to all essential items, beds, trays, hidey holes, feeding areas etc but i admit i dont have to do this with my 6, phew!
I dont know what Benevo is but if its like sand and kept deep then it would be your best bet to encourage digging