Sorry, my apologies, I was looking in the wrong spot.
First off, download your brushes, and unzip them, remembering where they are stored. Then, open up ABRViewer. You should get an interface that looks like this:
Click "Add another directory". Locate your downloaded brushes, most likely in your Downloads folder:
Then choose "Choose this Directory". Back in the ABRViewer, double-click the folder you now see. You'll get a dropdown where the brushes are. Click the drop down, then wait a few moments for the brushes to load:
Once you have your brushes loaded, close ABRViewer. Now go back PDN, and open up your CustomMiniBrushes. Click "Add Brushes", and look for your Downloads folder, then for the folder called "ABRViewImages":
Open that up, and you should see all of your brushes. Choose the ones you want to load, and hit enter. It'll take a while to load if you have a lot of brushes. I hope this helped (and was allowed).