[biggie5252]

I've never really come across noise due directly to Rcas, except maybe something you'd get at walmart that looks like it was made out of speaker wire. Even when routed down the same side of the car as power wire.

Almost always alternator whine is caused by a ground loop, if not faulty equipment.

Why does car audio not use digital as the norm? People don't care enough about the sound quality to pay for it. You would also have to have a DA converter in every amplifier, or make someone buy a stand alone converter.

There are plenty of upscale systems that use optical. Almost all dvd headunits have it. Alpine has a couple digital processors that take optical. Pioneer has/had a system that was completely digital back to the amps. It does exist and has since the late 80s/early 90s..