HT Omega Striker and Z5500 - digital or analog?

[viivo]

I'm a bit confused here since audio isn't really my thing.

Instead of going on for paragraphs about my current set-up and what I've been reading about DACs, I'll just say that I have the z5500s on the way and I am curious if I would get better sound quality in games by using the analog outputs or letting the sound card do onboard Dolby Digital/DTS encoding with the optical out.

Thanks.