I have the Oceanic Neo with the FDX-10 first stage. The difference between the FDX-10 and CDX-5 when I bought mine 4 years ago was the DVT. Only the FDX-10 came with it.
Now looking at the specs like Greg said, it appears the CDX-5 comes with the DVT now. Also, from doing some research, you can get the CDX-5 with and without an Environmental kit.
P.S I have never had any issues with my reg setup- NEO with the FDX-10.