Thanks for the explanation. So is there any point to installing a Hyperstar into an Edge? Or, which would be better, a non-Edge SCT with Hyperstar or an Edge with a reducer?
The choice between a regular SCT and an EdgeHD would depend on budget and just how critical you are about visual work.
A regular SCT with both a focal reducer and a Hyperstar would be the most flexible and budget friendly setup for video. The EdgeHD with a reducer or two would be a better choice for those who also want to do highly critical visual work. Regular SCTs are however certainly no slouches visually either, especially with a f6.3 reducer/corrector.
Using a C8 as an example you get a great range of focal lengths (and as Dr. Who mentioned just a great combination on an AVX mount). The f4 setup would likely be a stacked (f6.3 and .5x) reducer combination, a Meade f3.3 reducer, or something like the MFR-5 with spacers. The following numbers are approximate ...
Barlow (f20) - 4000mm planets, detailed lunar or solar
Native (f10) - 2000mm planets (moons), lunar or solar, small planetaries
Reducer (f6) - 1200mm smaller galaxies, planetaries, globulars
Reducer (f4) - 800mm popular nebulae, galaxies, large globulars, open clusters. This (and with the f6 reducer) create the most popular image scales with a 1/2" sensor camera.
Hyperstar (f2) - 400mm large extended nebulae, large galaxies
The value of the Hyperstar becomes apparent when you are planning on doing a lot of wider field work and don't have a small refractor or telephoto lens.
Personally if I was going to concentrate on EAA type of viewing and imaging I would look for a used but known good optically C8, and get an f6.3 SCT reducer. I'd use the money I saved to buy a better video/imaging camera and additional focal reducer. I'd look around for a bit more aggressive focal reducer to get f ratio down a bit more. After some experience with that type of setup I'd look to see if a Hyperstar makes sense. With C8s you won't have to worry about a fastar compatible secondary mirror even if you choose an older scope, there is always the Starizona adapter kit for those scopes that don't come with one (this isn't an option for a Meade 8").
For me it would be a tough decision between the Hyperstar and a separate 80mm refractor ... it would probably come down to how critical I was of the images I was getting and how much visual work I wanted to do.