The Intel iMacs are incredibly quiet and you don't have to pay for all the quirky extras. Even SPCR likes it a lot:
http://www.silentpcreview.com/article594-page1.html and
http://www.silentpcreview.com/article693-page1.html
"The 17" iMac has almost everything a silencer could want. It's quiet, efficient, good value (never thought we'd say that about an Apple), and it can even run Windows. It is also the only Core Duo-based "desktop" system currently available. We want one."
I spent a lot on huge heatsinks and $40 Papst 120mm fans and even rigged up a temperature-sensitive voltage switching device to cool down my homemade PC a few years back. Now I have an iMac, it's just as quiet as I achieved with all those specialist expensive parts but without the cost and stupid bother fixing shit all the time.
Good work on the Hush box, though. Those are awesomely cool, though you certainly end up paying for the clever design.