I would think that this heatsink would definately require air cooling, unless you put it vertical, so that the air can rise through it naturally. I think that it could easily cool a stereo aleph 5, given air cooling.
I'm using similar heatsinks in one of my amps. The fin spacing is even better and the fan is necessary. I bought one big piece and cut it in 4. Cost me $40.
The one on E-bay might be difficult to accomodate a fan. As you know the fans come in square sizes so if you put one directly on a sink, some fins will not be vented.