From what I have seen, the down pressure kit mounts on the post hole digger itself. It looks like it may have pressure for awhile, then the cylinder would need to be retracted and the auger run to the bottom of the hole, then apply the pressure again. I read it puts about 500 lbs of force down on the auger. I cant imagine how bad it would suck to have to dig your auger out that cork screwed into the ground like that. I believe you can still drill holes with this, without using the down pressure cylinder, so it would be just the weight of the auger. So for soft ground, you drill holes normally, and hard ground use the down pressure kit. I know this is not the perfect setup, but should work well for what I would be doing. If I had a skidsteer, I would go the same route you did. Putting enough down force on the auger to lift the skidsteer is alot. If you cant drill through it doing that, something is wrong. Here is the post hole digger I got.....
PD25 Series Post Hole Diggers | Land Pride