Pardon my ignorance, but what's the difference between a digital coax cable and a single plug RCA cable? The connectors look the same. Are they interchangable and if so, are they any consequences if using one for the other? What about the LFE subwoofer cable? They look like a single RCA cable too. Any difference? What I'm trying to understand is if there are actual differences in the cables and hence, the price differences, or if it's just a marketing thing. Thanks!