The BeoLab 8000s are such high-quality speakers that it would be a shame to feed them with the direct output of the in-built DAC (digital-to-analog-converter) in a Mac or in an iPod. These in-built DACs are OK but far from audiophile, while your speakers are.
I would recommend a stand-alone DAC between your laptop and your BeoLab 8000s. These you can get from about GBP 400 to GBP 1000 - the advantage being that you can run the digital signal from your laptop to the converter, and then run analog cables from that to your speakers.
For instance, if you get the Konnekt 24D from t.c.electronics you can go via Firewire from your laptop to the Konnekt, and then go via the Monitor Line-Out from that to your speakers, while having a volume control in the Konnekt that is very precise.