Photoshop opens RGBA EXR files without a problem.
This sounds like Maya is writing to channels with non-standard names, which Photoshop does not currently support.
I have used ProEXR and yes it reads extra channels.
Renaming the layers to nice labels and then setting the appropriate composite modes as they are loaded.
If you have ProEXR installed, it should become the default plug-in for opening EXR files. So you open the file and have layers, with which you may do whatever you wish.