Here is the only way to run long runs of line level audio; you have to use a sending and receiving "Balun" plus Cat5e/6 cable
http://muxlab.com/product/stereo-audio-balun
Buy the baluns, and make your own RCA cable for higher quality. The Cat5e/6 cable can be bought in various lengths. There will be no degradation.
The connection will be; RCA to balun (a few inches) 20 feet Cat 5e/6 to receiving balun, RCA (short) to line in.