個人想法:
有75ohm是最好, 但是用一般AV線的也是大有人在

From wiki:
http://en.wikipedia.org/wiki/RCA_connector

"While these are the standard colors found on commercially made products, same-colored cables may also be used. For example, a red cable may be used instead of a yellow one, as there is no other difference between them. There are generally two kinds of cables, for video (composite, component YPbPr and RGB) and digital audio 75 ohm impedance coax cable is recommended, for analog audio high impedance cable is recommended. Using high impedance cable for video and digital audio signals degrades signal quality, more noticeable with longer cables and with higher video resolutions. "