DAC hook up help

I believe that your DAC or your preamp will only allow you to choose one selection at a time, be it BNC, Coax, Toslink, Digital balance, so it should not matter. I have an optical (toslink) connection from my Touch to my DAC and a coax from my Mac mini to my DAC. I have to select optical or coax even if both sources are playing at the same time. This then goes to my preamp via analog rca connectors. I hope that this answers your question.

i have no switch or selector for different input

I am thinking Elizabeth is correct. For the price of the unit, it should to have automatic switching.

In my secondary family room system ,I use an older Stax Talent Dac .It has Optical and Coaxial digital inputs,Both inputs are used ,one on my Apple TV and the second on the Wadia 170i,there is a toggle switch on the Stax dac that switches between the two inputs so I can use one or the other but not both at the same time.I am sceptical about the auto switching and believe it will create conflict I much rather manual.
Regards
George