I tried it on two separate systems using xmms, one netbsd/i386 1.6.2
and the other netbsd/i386 1.6.  I went to xmms's preferences page,
selected the OSS output driver, configured it to use alternate 
devices /dev/sound1 and /dev/mixer1  (also tried using /dev/audio1
and /dev/mixer1).  audioctl confirms that these really are the devices
to which the usb iMic is attached.  all device permissions are 0666.

symptom: xmms thinks it's playing, but no sound comes out.

this is xmms 1.2.10 via pkgsrc

the iMic works fine, with the same amp and speakers, when I plug it 
into a MacOSX box.