Hi Roger
I have built this kit as too, well actually two sets of them! One is built with standard parts and the other set has all "premium boutique parts", the idea being that as this amp has such low THD I should be able to hear the difference (if any) of these parts and so I can decide for myself whether or not to use such things in future projects.
Getting back to your thread topic, I was in Jaycar just this afternoon looking at possible alternatives to the heat produced by this amp set up, don't forget the power supply either, as I have read that this also generates a lot of heat!
Jaycar has some nesting heatsinks that can be joined together, and there are some fans available with very low sound levels. My thoughts are to get a set of these and try to encase them within the chassis with some sort of casing that will reduce the noise levels of the fan by having the air input and output facing away from the listening position and having a small aluminium shield between the listening position and the inlet/outlet of the cooling fan. I don't know how effective this would be but would imagine that with a low noise fan and appropriate positioning of the shielding the noise level would not be intrusive.
It's worth a try! Let me know what ideas you can come up with!
Cheers
Bluesky