Not too sure about the cone, but as long as the angles are not overly extreme, it should be able to manipulate the blending curve to match with keystone as a curved mix.

It depends a bit on how the cone is being split up into projection zones as well....I would assume 4 across vertically and wrapped?

But as for Triple-Heads.....if there are only 4 projectors, then only one Triple-Head is needed....this will get three signals through one video output port, and the fourth will go out by itself from the second.

Make sure to have at least the ATI Radeon x1900XT video card with 512 MB to handle the processing of the Triple-Head.

Go for maximum blend overlap as well to get the best results on a curved projection surface.

I would recommend doing some sort of mock-up to try this to see if it does exactly what you need.

Hope this helps