Hi Mike,
The Z5500's are nice computer speakers, hardly audiophile equipment though. So, to get DD or DTS, you have to be linked with digital coax or optical to the card. It does not seem like the card has these, so to get these effects via analog, you'll have to run 3 stereo 3.5mm mini-jacks from soundacard outputs 1,2 and 3 to the yellow, black and green inputs on the Z5500's digital processor. The Processor will display "DTS" or "Dolby Digital" when it can decode the signal.
And yes, the speakers are too high. Put them level with your ears.