If that's what you have(wasn't sure if it was that or the pci version), you don't need the mixer. If you want/need to use all 4 preamps of the mixer, then i'd connect the main outs of the mixer to the line-ins of that interface, and just monitor from the outputs of that interface.
If you want to use both the outputs of the interface and mixer outputs(maybe for more headphones outputs), then you could go from the "1 main" output to the tape in of the mixer, and press the "tape to ctrl/hp" button on the mixer.
The SPDIF are digital inputs. These wont work. I mean the line(Mic/Hi-Z/Line) inputs.