Optical Cable, Optical Question: Length? Options

[Lord Pasty]

So i was down at Guitar Center today looking for a good length of Optical Cable, because my stereo that I use to monitor all my equipment is 5.1 capable. Logic Pro + MOTU 828 MkII also 5.1 capable. The thing is that I live with the g/f, and all the stuff kind of has to go in one room. (Yes, I know this isn't good for recording accoustics, but it's what I have for now).

To the question. He said that you couldn't find very long optical cable because digital cables loose their strength, or some such, with too much length? How true is that?