I think you are definitely on the right track with the Agnos MrotatorTCPS for using with the Canon 40D and Sigma 8mm Fisheye. The RingT is an option if you wish to shoot for batch stitching.

The advantage with the RingT is that it holds the lens and thus doesn't allow slight movement that can happen when the support is the camera (one screw). That said the disadvantage is that with the RingT you lose auto-focus. Still the Sigma 8mm is pretty in focus on everything when set to infinity anyway.

If you had been using a lighter plastic body camera like the Canon 400D/Rebel XTi or Nikon D40 I would have suggested the new Agnos MrotatorUM or MrotatorUT travel panohead. But because you are using the much heavier metal case 40D the MrotatorTCPS is the way to go.

Tripods worth considering are the Manfrotto range and Velbon Sherpa range. Another of quality is Gitzo. What you are looking for here is something stable with nice actions and a quality build. The Manfrotto 190XPROB is commonly used see more. I think the Velbon Sherpa 600R and 750R series are a better option though.

Consider also a quick leveling head. Like the Manfrotto #222 or Manfrotto #322RC2 etc.

Good luck with your shopping.

Regards, Smooth

The trick is to use the Manfrotto 323 Quick Release. (This is supplied with the MrotatorTCPS) and then you can simply release the camera and lens in one complete package. The Manfrotto 323 will keep the NPP correct. (You have to find it in the initial set-up)

Using the RingT the lens has to stay with the RingT on the panohead. (Assuming you are attaching the RingT to the MrotatorT) the RingT clamps to the lens in the position of the NPP (You have to find it in the initial set-up) and once tight you leave it there. You can detatch the camera and cap the lens at will. But the lens stays in place within the RingT. 

Another alternative is to use a RingT with RotatorMbase. Though you would not be able to shoot zenith and nadir shots.

Personally I feel you are best off with the MrotatorTCPS and add a RingT at a later date if you feel you need it.

Regards, Smooth