Upgrade Sound Card to Maximize Leviathan?

Hello,

I'm a long time "I use speaker" PC gamer, and recently decided to pick up a Leviathan. It "sounds" good, but now I feel like I'm not getting the most from it because I have an older Audigy Fx sound blaster card.

2 questions:
Am I not getting the full 5.1 (because there is a separate 3.5mm jack for rear channels and no optical out)?
Would I get much more if i picked up an optical out like a Z, Zx, ZxR card?

Assume price isn't a concern, I just want to make sure I get the most from my speaker purchase.

I appreciate your time!
Paul