Are you trying to go from the line outputs on the VL3D and into the DP-02? Sorry for the goofy question, but just trying to figure out what exactly you are wanting.
I would imagine you could use a pair of patch cables containing a pair of RCA (phono) to 1/4" TS (mono) ends. Connect the RCA ends to the line out of the VL3D. Connect the 1/4" to each of the 2 inputs of the DP-02. Make sure you set the switch next to input "A" to "line" instead of "guitar". You should be able to enable the inputs, assign a channel for each to record to, and monitor any feed from the VL3D before recording. Set your levels and you should be good to go.
I have no idea if this is too simplistic or not simple enough, as I'm not sure what your technical prowess is like. Let me know if you need any more info. Hope all works out!