I question why he is storing differnt songs on different keyboards. I would do that if I was not using a computer, but with the PC it's much easier if everything is stored there. This way you are using and getting a consistent method to output your music. My warning is that if you start chaining keyboards - and that includes the Digitech - then you increase and compound your chances of getting it WRONG. Also, playing live on one keyboard would have an effect on anything further UP the chain, but not prior.

In my experience the GM soundbanks of most top keyboards are both very good and very similar. Unless your friend is using modified soundmaps for special sounds, saving songs in separate keyboards is redundant and unnecessary. Unless your friend has a real need to use more than a couple keyboards, maybe he should consider consolidating.