BNC Info Please

I have so many options for connecting my transport, jitter reduction unit and DAC that it makes me dizzy... optical, balanced, S/PDIF digital and 75ohm BNC coaxial. With my current set up, my question is what is the difference between the BNC and S/PDIF outputs? I've been using a digital IC with a BNC adapter from the BNC out to my DAC's RCA input. This seems to provide the best detail (I assume because the BNC is true 75ohm). The same IC from the S/PDIF sounds less good to me. The only BNC IC I have looks pretty generic, dare I say industrial looking gives my DAC a little less refined sound than I'm used to. What are my options? Can BNC connections be had with higher quality coaxial? Does it make any difference? Is digital cable (with adapter) from the BNC out to the RCA in the best way to go? The only input options to my DAC are RCA and BNC. Any opinions on what the best way to go is? By the way, I'm not unhappy, my Resolution Audio Quantum DAC does a fine job, but enquiring minds just gots to know. Always looking for a better mousetrap. Thanks.