Firstly, if you go to file, preferences, components, you'll see a list of installed plug ins, including hopefully(!), foo_out_wasapi. Then, just go to preferences, playback sub menu, then output. At top of this menu should be output device drop down menu. from that list, there should be something like WASAPI: Dacmagic. Of course, select that!
Also, on output screen, you have a choice to select 16 bit, 24 bit, etc. I think it's recommended you set this to highest capabilities of your dac, so in your case, 24 bit. (for my dac, 16 bit, seriously considering a Dacmagic this year)
I read somewhere that it's beneficial to have the dither (slow) box ticked and the buffer length set to around 1000 ms. So i do.
Are you using some kind of lossless file format, by the way??
Hope any of this helps!