I've got a Steinburg UR22 interface and picked up some used Audix MM-15 passive monitors at my local brick and mortar. The interface has 1/4" monitor outputs but the monitors just take plain old speaker wire. The music store and Radioshack haven't been of much help, am I just gonna have to take a 1/4" cable, take off one adapter and connect the wires straight to the monitors?
The monitors you have are passive. They still need an amp to work. Buy an amp for $200 or better yet... get a modern pair of powered monitors. M-Audio 40s are around $130 and are a pretty good bang for the buck. Another $200 will get you some KRK Rokit 6s which are a nice step up.
If you really are on a tight budget get a Lepai a2020+, though a nicer pair of monitors like the ones suggested would work better imo.