I had this exact problem, the other day, to migrate a Cadstar design into Cadence Allegro, we thought a possible migration route might be through OrCAD Layout, but the problem is once you have a cadstar.pcb file you cannot back migrate this cadstar file to an older version i.e. (DOS .cdi) We spoke to Zuken about this and this was pretty much their answer, so looks like we cannot use OrCAD Layout as a migration route for modern cadstar files. The migration route we are considering is to reverse engineer the cadstar file into Allegro. We also spoke to Cadence about this, they have internal translators which take cadstar.pcb files to Allegro, but this would be done under their serives division and might be costly. So you pay your money and take your choice whether to pay Cadence or reverse engineer the PCB.