Does any one know if there is a limit to the length that an optical cable can be before the signal begins to degrade? I am in the process of connecting my i-mac via its optical output to my Musical Fidelity DAC, however my mac is around 6 to 7 metres from my Hi Fi. As an alternative, if this is too far away, is anyone aware of any reduction in sound quality using something like Airport Express. My unsubstantiated feelings tend to make me a little wary of wireless connectivity. Any views would be appreciated.