That is apples and oranges. RCA is an analog connection and optical is a digital connection. What components are you wanting to connect?
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Just like your misplaced question about 5.1 vs. 7.1 in the analog forum a few days ago, this question too is better suited in the Home Theater or Digital forums. You'll get more responses in those forums.
Also it may help to provide a little more info when asking a question too such as Digital Coax (that has an RCA connector) vs. Optical.