Both .nda and .nba files seems to be used as some sort of backup files by Nero BackitUp, so if any kind of interaction or nda to nba conversion is possible it would be done with this software. Unfortunately, we were not able to find information about this conversion between both file types, but if any program can work with them somehow, it would be Nero BackItUp.
Open NDA file Open NBA fileAs backup utility used to backup selected data, or operating system as well as hard drive