While I could make the Detector detect more than one thing, it would look clunky. Its supposed to be like the decider combinators except it reads from the network.
There is an alternative by setting up the detectors in a central location outputting the amount whenever the thing is above 0, and the routing the output onto the wires thats then on the power poles.
So that if you need to read an item you can just grab it from the power poles and put them into a decider combinator or to the IO bus. This way you only need one for each type.