Mate, it makes little difference to the panohead shooting with the equipment you have. Shooting 3 shots at 120 degrees with the Canon 5D and Sigma 8mm is correct and enough to complete a full 360x180 image "apart" from the tripod region.
If you are getting the "black triangle" at the zenith when the camera/lens is perfectly level you should tilt your camera up around 4 to 7 degrees until this area closes. Using "Smartblend" plug-in will deal with all the blending necessary for a good Zenith so long as you are set perfectly on the NPP lens entrance pupil.
You cannot under any circumstance not include the tripod/panorama head, all you can do is minimize it and then either clone & heal it out of the image or shoot a down/bottom (Nadir) shot and stitch or patch it in. This because the lens is 180 degrees and will always capture part of this area in the photograph. Tilting the camera/lens up the 4 to 7 degrees to cover the Zenith fully will also open up the tripod/pano head hole. This is normal.
So what is the advantage of the Agnos MrotatorTCPS and the Nodal Ninja 3 panorama heads? Quite simply the Agnos will allow a Battery Grip and is a more sturdy unit with far more options. But when it comes to shooting nothing much is different.
Setting the NPP on either panohead is the same. You need to adjust over the X & Y axis until you have minimized error. Getting a perfectly round circle when looking down upon the tripod/panohead in a panorama is the fast guide and if you want to take it further you should publish to .psd layers and crop out and part of the overlap join area and using the two layers of that seem move one layer and count the pixels to make it perfect (could be in X & Y) directions. Keep adjusting on the panohead taking notes until such time you have it perfected. (well as close as you can) I got mine down to (2) horizontal pixels and that for me is close enough.
All this and you will still need to do some small Photoshop editing to produce a final finished panorama close to perfection.
There is no magic bullet.