If you're using Logic Pro to create your tracks, just follow the directions below to export them as 320 kbps MP3 files.

When exporting from Logic Pro, you'll first need to select the section of your audio file that you want to export. Once you have that selected, click File at the top of the program,  then click Bounce > Project or Section.

After clicking that, a Bounce window will pop-up. Within that window, be sure to select MP3 as your Destination in the top left corner. In that same corner, also be sure that MP3 is highlighted in blue by clicking on it. Once it's highlighted, you'll be able to set the parameters or your MP3.

When MP3 is highlighted, you'll see the field Bit Rate Stereo. Use the Bit Rate Stereo drop-down menu to select 320 kbps. Once that's done, click the OK button at the bottom of the window. 

After clicking OK, you'll be able to select your download location. Once you do that and save it, your audio file will be saved and you'll be all set to upload it to Digital DJ Pool :)