What are all these different output jacks for?

Like you said, the digital outs are for use with outboard DACs or receivers with built in DACs (3 different types of connections). The RCA analog outputs are standard, unbalanced and the XLR are balanced. If your Unico has XLR inputs, you could try connecting it that way to see if it sounds better than the RCA jacks. It should, but it depends on the design of the two pieces. If the circuitry isn't balanced, it may be a waste of time. XLR jacks don't necessarily mean that the circuitry is balanced.

Phil prety much said it all. As far as the other outputs go, you will find numerous threads discussing the values of Optical (that's fibre optics...glass interconnects are much better than plastic), coax which there seems tp be a slight(?)preponderance of belief is better than optical and AES/EBU which many (although not all of us...) consider better than coax. These are all digital outputs for use in another DAC. If you were to get a really nice DAC, you can run one component into it via optical, another via coax and the third via AES. That your component has all three outputs just allows you to chose which one you want to use.

Hey Shoe, how do you like the Ospreys?
I've been looking at upgrading to them from the Shearwaters, but am not sure...can you give me your opinion on them?
Thanks
Tuan