This is how I handled this problem on my Firebox:
[image: Cbf4rOql.jpg]
(excuse the dust, this was literally just pulled out of service an hour ago, it just happened to be still on my living room floor)
My roommate had a random low-profile copper heat sink sitting around, so that plus some thermal epoxy (a heat sink clip tab was broken in the process of disassembling the thing) and a 120mm hole cut directly above it kept this idling at 47C constant. The 60mm CPU fan and 3x 40mm rear fans were all removed, the 120 on top is the only fan in use.
It went from screaming to silent as a result of this conversion.