Can a 75 ohm digital rca cable be used in place of a regular rca interconnect?

Interesting... so if anything bc of the impedance it might lower the volume/signal?

Nominal impedance is so because of the specific operating frequency that the measurements are taken. Obviously, a cable designed to convey a 500MHz Manchester encoded digital signal will be capable of conveying audio spectrum just as well, but noise rejection is not a strong suit of unbalanced cables to begin with. Better quality cables are made with two inner conductors (a pair) of the same wire, and an outer foil shield surrounded by 100% braided shield with a drain wire. The two inner conductors go to the signal hot and signal ground respectively on each side, and the drain wire is either connected to signal ground on the source side, or (better) to chassis ground to protect from noise infiltration on both of the signal carrying conductors. The only way to improve on this is taking the leap to XLR connectors and fully balanced differential circuits, but that’s not always practical to do. 

Interesting... so if anything bc of the impedance it might lower the volume/signal?

No not at all.  75 ohm is the characteristic impedance of a coax cable.  Google it for a proper technical explanation.  

@loomisjohnson 

You are going to be concerned about frequency spectrum and bandwidth with 15kHz analog video (which is obsolete) much, much, much more than with analog audio. Noise rejection is another thing that lowly unbalanced analog audio cables fare poorly at. 

@rotarius 

No not at all. 75 ohm is the characteristic impedance of a coax cable. Google it for a proper technical explanation.  

Nope. Not even remotely correct. Coaxial cables come in more than one characteristic impedance, and that is “Z” for impedance, not resistance, which is a static value, regardless of the operating frequency range. There are many more different coaxial cable impedance specs as there are hat sizes.  Two of the more common values are 50 ohm and 75 ohm. Impedance is what describes the dynamic, frequency-affected component due to capacitive and inductive reactance.