if you connect the soundblaster up via optical to your amp, you're effectively bypassing the dac in the soundcard and pretty much running it how you have it now - using the dac in tha amp, so you probably won't notice any difference.
If you want to try the soundcard dac, you'll have to take the analogue out from the soundcard in to the amp. Do that, then you can compare the two and see which one you prefer.
If neither are floating your boat, you can either look at getting one of the pro soundcards such as the m-audio, presonus and the like, or go down the hifi dac route.