Check out Todd's note as suggested. You don't need any additional CoDec. If they are from P2 cards/ disks, AE will import your files natively. If they are not, than this is a no go, regardless how many CoDecs you install. Just like OMF (or AVI or MOV), MXF is merely a container format that can contain any number of streams and additional data. Because of that, there is no way to understand any variation on the theme per se and provide a generic I/O handler. unless Avid and the others don't publish their internal specs and extensions, this will not change, as much as you and I may not like it. Adobe can only work based on what's available and properly documented.
Mylenium