Analog or Digital? Z5500

I just bought the Z5500 (awesome system for $$, actually pretty awesome anyway).

So far I've got it connected to my GA-P35-DS3L mother board with the 3 jacks (orange, black, and green) it comes with. I understand this an analog connection. My mother board also has an optical out.

As I understand it, the optical connection will transfer the digital signal directly to the Z5500 for decoding.
So which is better? The Z5500 DAC's or the Mobo's onboard audio DAC's?

I use the speakers for gaming and playing music, but mostly gaming.

Most games have discrete sound channels, which means you will only get surround from analog output. There are only a select few games with the ability to output Dolby Digital 5.1, unlike consoles, which exclusively output with encoded digital formats.