i do just that with my edifiers, and a xonar DG, the DG's set to 5.1 speaker mode and the flexbass mode switched on (actes as a LFE crossover) @120hz. my amp has a built in crossover as well witch i think is what Temi means. you dont need one if the DS has the flexbass.
the sub plugs into the center/sub of you sound card sorted.