Once you have the file inside MC version 6, this is very simple and straightforward:
Select the clip in the bin (or the timeline you created), and choose File->Export, and choose MXF Op1A from the menu. Then, when asked, choose XDCAM-HD and 50MBits/s.
However, you will need to bring the file into MC. And you will need to check if everything is OK, mostly color space (especially since this comes from FCP) and field order.
I would create a 1920×1080/50i project in Avid. Then Choose File->Link to AMA file, and specify your source clip.
The color corrector features a Y-Waveform and a Vectorscope if you need to check levels (toss the clip in a sequence first).
If the levels appear to be wrong, go to the bin, select the clip and choose Clip->Source Settings, and specify the source’s color space there.
Check field order to be sure, and timecode too, since your specifications seem to require some timecode (would be nice to know which).