How exactly do you "specify" the component you want to decode? Say you had a receiver and a dvd player with dolby and dts, how would you use the dvd's dacs and vice versa?
If you want the DVD player to decode(provided it has built in decoders), you run from the six-channel analog outs to the six-channel analog ins on the receiver and select that input.
For the receiver to do the decoding, just run a digital cable(toslink or coxial)from the DVD player into the receiver.