I am no expert but I believe the main advantage of optical is that it should have WAY less interference then a normal wire, as you stated. I don't know enough to say for sure that it will be better then balanced XLR but I would assume this is the case.

A slighlty different discussion might be that XLR is better because it is analog (warmer and all that jazz) and not digital (forcing the signal to be discrete). So before people start praising the holyness that is analog let me just remind you all that in this modern era nearly all music is recorded and mixed digitally in the first place.

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This is a more complex problem than perhaps you first thought.

Digital signals experience no interference as such; you won't get static or any sort of a hum. This is because the signal is coded into binary 1's and 0's, which either get through or don't. If they don't, then they will be retransmitted. In short, you will get out of one end exactly what you put in the other end with no loss.

Analogue signals, even balanced ones, are prone to interference. Electromagnetic radiation (radio, TV, microwave, whatever) and magnetic fields, such as those produced by mains electrical cabling, can induce a (small) current into the wire which will affect the signal coming through it. This equates to interference (static and hum). However, balanced signals (balanced XLR and jacks) are designed in such a way that the interference acts on the signal twice, but in opposite directions simultaneously, thus cancelling each other out, and only very very small amounts of interference gets through.

Now we come on to the subject of digital encoding. Some digital signals are better than others. This depends on both the bitrate and sampling frequency used, and the quality of both the analogue to digital converter (ADC) at one end and the digital to analogue converter (DAC) at the other end. The quality of ADC's in DJ mixers is *invariably* shite, and will only encode at 44.1 kHz with 16 bit samples. This is the same as a standard CD. This is arguably worse than an analogue signal from a mixer (there are many many threads on this subject), and for proper professional digital recording you should be looking at 96 kHz and 24/48 bit samples.

Bearing in mind that to use a digital signal you must first convert the analogue signal into a digital signal (which loses some of the quality of the original) and then convert it back to analogue to send to the speakers (which creates more loss), keeping in mind that balanced analogue is very resistant to interference and noise, I would personally go with balanced XLR's rather than optical coax.