Ok, to do this achievement, do the following:
Main Menu ===> Game Modes
Game Modes ===> Tournament Mode
Tournament Mode ===> Create Tournament
Set the tournament to the following:
Number Of Team: 64
Auto Fill Teams: No
Tournament Name: (whatever you want, I left mine blank)
Advanced Settings: On
On the next page, just change the "Fixtures V Each Team" to 1.
When filling in the teams, pick someone good like Man United, Chelsea, Barcelona, Inter Milan etc. Then for all the other teams choose teams from Coca Cola League 2 in England. From here on, you can either play all 6 matches or... sim all your matches.
If you've followed what I mentioned to do when choosing teams this should be easy, but just incase, save your game before every match. If you sim and lose, immediately turn your Xbox off if you have autosave enabled. Easier if you turn of autosave and just save after every win and reload if you lose.