Magma PE6R4 is the only official one, though there are 2 versions of it.
The current one (the -I) and the original which vary by the type of cable connector.
You asked where you can find a list, that's not so easy.
There is this
http://akmedia.digidesign.com/suppor...v803_63872.pdf
Unfortunately you have to have been following along to know that avid has stated the Magma chassis is supported today and will be for the foreseeable future. If you were to look at the Protools HD Product page and follow the link to expanded systems you would only find the PCIe to PCIe product. That doesn't inspire a lot of confidence does it?