After the Generous donation of a v1.6b Xbox from Team Xecuter I was able to narrow down (with a lot of help from 'dmp' and a lot of help from random stabbing in the dark) the cause of Cromwell not booting on these Xboxes. So here's Gentoox Loader v4.7 which seems to boot fine on all Xboxes. Give it a try and let me know!