This highly specialized piece of gear makes a world of difference in recording sound with the D4/ D800. The DXA-SLR Pro is a phantom power source needed with a number of different mics. You have the same two options I had when delving into this thing, you can either go and learn all your can on the subject or just trust someone and dive in. I trusted my good friend Scott and dove in. Darn if he wasn’t right, this thing rocks!