PE serial number #1063

I'm currently running PE firmware 4.8 but I'd like to be able to switch between 5.0 and the latest 6.x build, mostly to have PG-200 functionality with my MKS-30 but I'd still like to use the PE with my JD-990 on occasion.  Was PG-200 protocol too buggy to continue supporting it?

Is there an archive somewhere of 5.0?

Does downgrading to a lower firmware cause compatibility issues with the current bootloader?

And finally, would there be a way to write a custom PE firmware editor that let you mix and match which synths you want?   I'd even entertain contracting Murray to compile a one-off custom firmware if the editor isn't feasible.