As discussed, here are some testable sgi images. All were generated with the Maya 5.0 standard renderer (NOT Mental Ray).
Naming is:

Format_bitdepth_channels.sgi

rgb= obvious channels
a=alpha channel
d=depth channel

The depth channel *should* be the same bit depth as the other channels. When I get a chance, I will send you this same series of files from MentalRay's renderer. MR uses floating point (32-bit depth, i believe) for it's depth channels, and this totally screws up every viewer on the planet. I've yet to see a viewer that can load it.

Let me know if I can provide any other test images!
-Sam