Great and very important questions Dkrugler!
If your Horotec screwdrivers have straight blades then you can use a standard holder. I’ll try to find some links to this tool and all others that I mention in this post and will put them up here in an hour or so. If they are the “hollow ground” (concave) blade (I believe they offer both) then Horotec makes a sharpener that will maintain this blade radius while keeping the grind lines running horizontal to the blade bottom. Problem is that the tool is very expensive. Most of my screwdrivers are straight edged but I do have some that are hollow ground and like to maintain the same shape when possible. For this type of blade I usually use my Foredom flex tool with fine sanding cylinders (Got mine from a machinery supply house but I think Dremel has them too) which does a pretty good job for me. This runs the abrasion lines vertically though. When finished I just manually draw the blade along the length of the cylinder enough to change the grain direction. For straight edged blades grinding I use a FINE 2″ x 6″ Indian stone. If you like a more polished blade you can then repeat the process with a White Hard Arkansas stone.
I use the same stones mentioned above for grinding gravers. For normal or rough cutting I just use the gravers sharpened with the Fine 2″x 6″ Indian stone. For finishing cuts I use gravers that have been finished with the white Ark. stone.
Heading out the door right now (grocery store run) but will grab some links to these tools and post them up here when I get back.