I searched and searched but didn't find anyone else posting anything similar. So if this is a re-post, tough.
I only cracked it yesterday, just in time for the races tonight.
What I used:
A Season Pass from MotoGP. Bought one the first year, didn't want to pay for another one until now. 99 Euro
A 2011 Mac Mini running Lion, latest update of course.
AppleTV 3. $99 or 109 Euro.
HDMI cable from AppleTV to Sony 720p flatscreen.
Airport Extreme wi-fi base station.
AirParrot - $9.99 - with the latest update. This is important because the previous version couldn't stream audio. Since my Mac is separated from my TV by a concrete ceiling, a cable was not an option. AirParrot now does stream audio since the update yesterday, works like a charm. The audio on the Mac stops though but that's a minor glitch since the sound is coming from your TV/Home Cinema anyway.
That's all there is to it. I couldn't stream from my iPad 1st generation via AirPlay, most likely because the CPU can't cut it. On the Mac, Flash Player is already running away with 35% of my CPU which is a lot.
AirParrot will be redundant as streaming wirelessly will be included in Mountain Lion which comes out this summer. But for now, I'm glad it works.