Leogang & Hinterglemm were the best riding venues when we stayed in Zell a couple of years ago.
You can buy a day lift pass that opens up some fantastic epic rides. There is/was a Kona centre at Leogang (we rented Kona Stabs for a great day in the bike park, and some hardtails for long day rides) and they provided all the route guides.
I would happily go there again, and save Kaprun for a dull afternoon's snowboarding in August.
A one-time forum regular DizinAustria ran Over the Edge, I think. Other posters might still know of Diz. If not, this looks a link to start you off.
http://www.club-giraffe.com/location.asp?catID=32&subID=40