I have the Hercules 4-Mx and have the audio routing setup as below.
Sound setup.jpg
The Hercules mk4 should have a similar audio setup, so just copy my settings. Also you need to change the sound card.
Choose "Hercules DJ Console MK4 ASIO" from the drop down.
Hope that helps
*EDIT*
If you see no option for the MK4 ASIO, then all you have to do is close Cross, open the Hercules Control Panel, go the the ASIO tab and click on the ASIO circle (it should turn green or blue, I can't quite remember).
After this is done the you should see the MK4 ASIO option in Cross.
You do not have the required permissions to view the files attached to this post.