What to do with users who get software mode in Stage3d?

I've got a Stage3d AIR game compiled as a desktop exe using ADT and distributed through Steam. About 3% of users are being thrown into super-slow Software Mode. Most of them have relatively new video cards and up to date drivers, and they can play other 3d games. Some use NVIDIA, some ATI, some AMD, different versions of windows etc. My game instantiates a series of contexts determine the optimum stage3d profile but all of them fail to connect to the gpu for these users, even baselineConstrained. I am not using requestContext3DMatchingProfiles because it throws errors.

I need advice on how to approach this issue. I started collecting dxdiags and filed a bug, but since the cards are so disparate and I suspect the issue is with their particular systems and not the hardware itself, I'm not sure that's going to be useful. Obviously I tell them to update their drivers and make sure they're using the right card on dual-card systems (eg Nvidia Optimus). But when that doesn't work, what next?

Is there a standard test for stage3d compatibility that I could point these users towards?